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 $54.81   5.789%   $57.983   $57.98   $58.00   $58.00  
  Purchase #2 $110.66   9.461%   $121.1295   $121.13   $121.15   $121.10  
  Purchase #3 $105.83   11.830%   $118.3497   $118.35   $118.35   $118.30  
  Purchase #4 $209.72   7.356%   $225.147   $225.15   $225.15   $225.10  
  Purchase #5 $66.83   12.847%   $75.4157   $75.42   $75.40   $75.40  
  Purchase #6 $127.32   13.372%   $144.3452   $144.35   $144.35   $144.30  
  Purchase #7 $59.40   9.276%   $64.9099   $64.91   $64.90   $64.90  
  7 purchase totals = $734.57       $807.2800   $807.29   $807.30   $807.10