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 $43.26   13.543%   $49.1187   $49.12   $49.10   $49.10  
  Purchase #2 $232.94   10.503%   $257.4057   $257.41   $257.40   $257.40  
  Purchase #3 $58.60   10.571%   $64.7946   $64.79   $64.80   $64.80  
  Purchase #4 $197.68   9.642%   $216.7403   $216.74   $216.75   $216.70  
  Purchase #5 $208.84   12.143%   $234.1994   $234.20   $234.20   $234.20  
  Purchase #6 $168.27   13.822%   $191.5283   $191.53   $191.55   $191.50  
  Purchase #7 $24.91   9.761%   $27.3415   $27.34   $27.35   $27.30  
  7 purchase totals = $934.50       $1,041.1285   $1,041.13   $1,041.15   $1,041.00