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 $174.54   5.447%   $184.0472   $184.05   $184.05   $184.00  
  Purchase #2 $221.44   3.791%   $229.8348   $229.83   $229.85   $229.80  
  Purchase #3 $244.86   8.559%   $265.8176   $265.82   $265.80   $265.80  
  Purchase #4 $167.71   6.837%   $179.1763   $179.18   $179.20   $179.20  
  Purchase #5 $110.51   12.356%   $124.1646   $124.16   $124.15   $124.20  
  Purchase #6 $91.46   11.653%   $102.1178   $102.12   $102.10   $102.10  
  Purchase #7 $228.90   5.872%   $242.341   $242.34   $242.35   $242.30  
  7 purchase totals = $1,239.42       $1,327.4993   $1,327.50   $1,327.50   $1,327.40