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 $118.40   11.617%   $132.1545   $132.15   $132.15   $132.20  
  Purchase #2 $216.54   8.164%   $234.2183   $234.22   $234.20   $234.20  
  Purchase #3 $183.48   9.620%   $201.1308   $201.13   $201.15   $201.10  
  Purchase #4 $121.29   10.278%   $133.7562   $133.76   $133.75   $133.80  
  Purchase #5 $103.98   10.802%   $115.2119   $115.21   $115.20   $115.20  
  Purchase #6 $150.84   7.540%   $162.2133   $162.21   $162.20   $162.20  
  Purchase #7 $53.41   5.292%   $56.2365   $56.24   $56.25   $56.20  
  7 purchase totals = $947.94       $1,034.9215   $1,034.92   $1,034.90   $1,034.90