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 $88.48   8.787%   $96.2547   $96.25   $96.25   $96.30  
  Purchase #2 $40.35   6.582%   $43.0058   $43.01   $43.00   $43.00  
  Purchase #3 $85.77   3.244%   $88.5524   $88.55   $88.55   $88.60  
  Purchase #4 $68.65   8.105%   $74.2141   $74.21   $74.20   $74.20  
  Purchase #5 $42.25   4.220%   $44.033   $44.03   $44.05   $44.00  
  Purchase #6 $250.38   10.383%   $276.377   $276.38   $276.40   $276.40  
  Purchase #7 $126.56   9.662%   $138.7882   $138.79   $138.80   $138.80  
  7 purchase totals = $702.44       $761.2252   $761.22   $761.25   $761.30