Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $200.57   3.415%   $207.4195   $207.42   $207.40   $207.40  
  Purchase #2 $244.72   6.268%   $260.059   $260.06   $260.05   $260.10  
  Purchase #3 $157.82   6.332%   $167.8132   $167.81   $167.80   $167.80  
  Purchase #4 $113.67   7.314%   $121.9838   $121.98   $122.00   $122.00  
  Purchase #5 $158.93   3.229%   $164.0618   $164.06   $164.05   $164.10  
  Purchase #6 $184.41   12.578%   $207.6051   $207.61   $207.60   $207.60  
  Purchase #7 $232.32   12.282%   $260.8535   $260.85   $260.85   $260.90  
  7 purchase totals = $1,292.44       $1,389.7959   $1,389.79   $1,389.75   $1,389.90