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 $219.35   12.387%   $246.5209   $246.52   $246.50   $246.50  
  Purchase #2 $219.86   7.308%   $235.9274   $235.93   $235.95   $235.90  
  Purchase #3 $153.62   3.111%   $158.3991   $158.40   $158.40   $158.40  
  Purchase #4 $241.32   6.701%   $257.4909   $257.49   $257.50   $257.50  
  Purchase #5 $103.61   7.534%   $111.416   $111.42   $111.40   $111.40  
  Purchase #6 $122.94   12.544%   $138.3616   $138.36   $138.35   $138.40  
  Purchase #7 $210.62   4.262%   $219.5966   $219.60   $219.60   $219.60  
  7 purchase totals = $1,271.32       $1,367.7125   $1,367.72   $1,367.70   $1,367.70