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 $109.26   12.505%   $122.923   $122.92   $122.90   $122.90  
  Purchase #2 $61.92   10.316%   $68.3077   $68.31   $68.30   $68.30  
  Purchase #3 $204.81   13.599%   $232.6621   $232.66   $232.65   $232.70  
  Purchase #4 $195.42   6.228%   $207.5908   $207.59   $207.60   $207.60  
  Purchase #5 $131.48   5.757%   $139.0493   $139.05   $139.05   $139.00  
  Purchase #6 $195.99   7.726%   $211.1322   $211.13   $211.15   $211.10  
  Purchase #7 $194.85   12.857%   $219.9019   $219.90   $219.90   $219.90  
  7 purchase totals = $1,093.73       $1,201.5670   $1,201.56   $1,201.55   $1,201.50