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 $43.94   9.409%   $48.0743   $48.07   $48.05   $48.10  
  Purchase #2 $159.33   13.616%   $181.0244   $181.02   $181.00   $181.00  
  Purchase #3 $62.29   6.671%   $66.4454   $66.45   $66.45   $66.40  
  Purchase #4 $12.71   5.298%   $13.3834   $13.38   $13.40   $13.40  
  Purchase #5 $63.49   6.373%   $67.5362   $67.54   $67.55   $67.50  
  Purchase #6 $245.53   11.532%   $273.8445   $273.84   $273.85   $273.80  
  Purchase #7 $197.91   9.447%   $216.6066   $216.61   $216.60   $216.60  
  7 purchase totals = $785.20       $866.9148   $866.91   $866.90   $866.80