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 $201.53   7.485%   $216.6145   $216.61   $216.60   $216.60  
  Purchase #2 $211.97   3.480%   $219.3466   $219.35   $219.35   $219.30  
  Purchase #3 $20.43   11.549%   $22.7895   $22.79   $22.80   $22.80  
  Purchase #4 $237.61   3.554%   $246.0547   $246.05   $246.05   $246.10  
  Purchase #5 $132.49   6.848%   $141.5629   $141.56   $141.55   $141.60  
  Purchase #6 $47.86   13.437%   $54.2909   $54.29   $54.30   $54.30  
  Purchase #7 $133.99   11.659%   $149.6119   $149.61   $149.60   $149.60  
  7 purchase totals = $985.88       $1,050.2710   $1,050.26   $1,050.25   $1,050.30