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 $232.74   10.551%   $257.2964   $257.30   $257.30   $257.30  
  Purchase #2 $224.61   6.261%   $238.6728   $238.67   $238.65   $238.70  
  Purchase #3 $201.62   5.625%   $212.9611   $212.96   $212.95   $213.00  
  Purchase #4 $184.73   6.217%   $196.2147   $196.21   $196.20   $196.20  
  Purchase #5 $231.71   5.359%   $244.1273   $244.13   $244.15   $244.10  
  Purchase #6 $98.59   9.732%   $108.1848   $108.18   $108.20   $108.20  
  Purchase #7 $85.76   9.290%   $93.7271   $93.73   $93.75   $93.70  
  7 purchase totals = $1,259.76       $1,351.1842   $1,351.18   $1,351.20   $1,351.20