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 $178.77   8.508%   $193.9798   $193.98   $194.00   $194.00  
  Purchase #2 $61.67   3.682%   $63.9407   $63.94   $63.95   $63.90  
  Purchase #3 $151.35   12.323%   $170.0009   $170.00   $170.00   $170.00  
  Purchase #4 $238.68   7.407%   $256.359   $256.36   $256.35   $256.40  
  Purchase #5 $61.75   7.633%   $66.4634   $66.46   $66.45   $66.50  
  Purchase #6 $38.91   3.715%   $40.3555   $40.36   $40.35   $40.40  
  Purchase #7 $241.66   13.113%   $273.3489   $273.35   $273.35   $273.30  
  7 purchase totals = $972.79       $1,064.4482   $1,064.45   $1,064.45   $1,064.50