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 $56.66   5.527%   $59.7916   $59.79   $59.80   $59.80  
  Purchase #2 $161.75   11.127%   $179.7479   $179.75   $179.75   $179.70  
  Purchase #3 $241.61   11.751%   $270.0016   $270.00   $270.00   $270.00  
  Purchase #4 $236.73   3.428%   $244.8451   $244.85   $244.85   $244.80  
  Purchase #5 $106.48   12.390%   $119.6729   $119.67   $119.65   $119.70  
  Purchase #6 $129.44   11.840%   $144.7657   $144.77   $144.75   $144.80  
  Purchase #7 $226.74   13.332%   $256.969   $256.97   $256.95   $257.00  
  7 purchase totals = $1,159.41       $1,275.7938   $1,275.80   $1,275.75   $1,275.80