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 $203.84   12.366%   $229.0469   $229.05   $229.05   $229.00  
  Purchase #2 $119.77   9.846%   $131.5626   $131.56   $131.55   $131.60  
  Purchase #3 $138.78   5.859%   $146.9111   $146.91   $146.90   $146.90  
  Purchase #4 $154.56   7.343%   $165.9093   $165.91   $165.90   $165.90  
  Purchase #5 $182.77   10.312%   $201.6172   $201.62   $201.60   $201.60  
  Purchase #6 $169.38   11.233%   $188.4065   $188.41   $188.40   $188.40  
  Purchase #7 $121.40   5.620%   $128.2227   $128.22   $128.20   $128.20  
  7 purchase totals = $1,090.50       $1,191.6763   $1,191.68   $1,191.60   $1,191.60