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 $233.62   5.810%   $247.1933   $247.19   $247.20   $247.20  
  Purchase #2 $149.38   4.203%   $155.6584   $155.66   $155.65   $155.70  
  Purchase #3 $123.56   5.281%   $130.0852   $130.09   $130.10   $130.10  
  Purchase #4 $235.73   11.323%   $262.4217   $262.42   $262.40   $262.40  
  Purchase #5 $53.59   11.550%   $59.7796   $59.78   $59.80   $59.80  
  Purchase #6 $83.47   4.614%   $87.3213   $87.32   $87.30   $87.30  
  Purchase #7 $246.68   8.327%   $267.221   $267.22   $267.20   $267.20  
  7 purchase totals = $1,126.03       $1,209.6805   $1,209.68   $1,209.65   $1,209.70