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 $146.85   11.791%   $164.1651   $164.17   $164.15   $164.20  
  Purchase #2 $242.57   7.321%   $260.3285   $260.33   $260.35   $260.30  
  Purchase #3 $62.91   6.465%   $66.9771   $66.98   $67.00   $67.00  
  Purchase #4 $152.29   11.112%   $169.2125   $169.21   $169.20   $169.20  
  Purchase #5 $60.89   11.647%   $67.9819   $67.98   $68.00   $68.00  
  Purchase #6 $238.70   13.459%   $270.8266   $270.83   $270.85   $270.80  
  Purchase #7 $155.93   10.103%   $171.6836   $171.68   $171.70   $171.70  
  7 purchase totals = $1,060.14       $1,171.1753   $1,171.18   $1,171.25   $1,171.20