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 $147.45   12.224%   $165.4743   $165.47   $165.45   $165.50  
  Purchase #2 $183.44   6.665%   $195.6663   $195.67   $195.65   $195.70  
  Purchase #3 $59.79   7.530%   $64.2922   $64.29   $64.30   $64.30  
  Purchase #4 $178.86   11.413%   $199.2733   $199.27   $199.25   $199.30  
  Purchase #5 $89.55   8.450%   $97.117   $97.12   $97.10   $97.10  
  Purchase #6 $243.68   13.727%   $277.13   $277.13   $277.15   $277.10  
  Purchase #7 $141.50   8.368%   $153.3407   $153.34   $153.35   $153.30  
  7 purchase totals = $1,044.27       $1,152.2938   $1,152.29   $1,152.25   $1,152.30