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 $61.49   3.360%   $63.5561   $63.56   $63.55   $63.60  
  Purchase #2 $92.71   12.435%   $104.2385   $104.24   $104.25   $104.20  
  Purchase #3 $50.92   4.652%   $53.2888   $53.29   $53.30   $53.30  
  Purchase #4 $78.51   11.172%   $87.2811   $87.28   $87.30   $87.30  
  Purchase #5 $200.41   5.603%   $211.639   $211.64   $211.65   $211.60  
  Purchase #6 $155.70   4.856%   $163.2608   $163.26   $163.25   $163.30  
  Purchase #7 $147.32   10.652%   $163.0125   $163.01   $163.00   $163.00  
  7 purchase totals = $787.06       $846.2768   $846.28   $846.30   $846.30