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 $84.61   9.834%   $92.9305   $92.93   $92.95   $92.90  
  Purchase #2 $86.82   9.618%   $95.1703   $95.17   $95.15   $95.20  
  Purchase #3 $187.85   11.253%   $208.9888   $208.99   $209.00   $209.00  
  Purchase #4 $204.38   13.484%   $231.9386   $231.94   $231.95   $231.90  
  Purchase #5 $222.96   10.635%   $246.6718   $246.67   $246.65   $246.70  
  Purchase #6 $215.74   10.500%   $238.3927   $238.39   $238.40   $238.40  
  Purchase #7 $190.80   9.248%   $208.4452   $208.45   $208.45   $208.40  
  7 purchase totals = $1,193.16       $1,322.5379   $1,322.54   $1,322.55   $1,322.50