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 $66.70   13.203%   $75.5064   $75.51   $75.50   $75.50  
  Purchase #2 $231.77   8.106%   $250.5573   $250.56   $250.55   $250.60  
  Purchase #3 $30.78   6.398%   $32.7493   $32.75   $32.75   $32.70  
  Purchase #4 $101.62   9.153%   $110.9213   $110.92   $110.90   $110.90  
  Purchase #5 $149.90   12.343%   $168.4022   $168.40   $168.40   $168.40  
  Purchase #6 $120.57   11.215%   $134.0919   $134.09   $134.10   $134.10  
  Purchase #7 $229.26   4.754%   $240.159   $240.16   $240.15   $240.20  
  7 purchase totals = $930.60       $1,012.3874   $1,012.39   $1,012.35   $1,012.40