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 $150.77   12.407%   $169.476   $169.48   $169.50   $169.50  
  Purchase #2 $49.69   10.276%   $54.7961   $54.80   $54.80   $54.80  
  Purchase #3 $88.70   11.388%   $98.8012   $98.80   $98.80   $98.80  
  Purchase #4 $58.54   4.355%   $61.0894   $61.09   $61.10   $61.10  
  Purchase #5 $55.79   4.474%   $58.286   $58.29   $58.30   $58.30  
  Purchase #6 $173.91   6.252%   $184.7829   $184.78   $184.80   $184.80  
  Purchase #7 $213.95   6.642%   $228.1606   $228.16   $228.15   $228.20  
  7 purchase totals = $791.35       $855.3922   $855.40   $855.45   $855.50