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 $61.76   8.506%   $67.0133   $67.01   $67.00   $67.00  
  Purchase #2 $217.59   6.281%   $231.2568   $231.26   $231.25   $231.30  
  Purchase #3 $38.98   8.144%   $42.1545   $42.15   $42.15   $42.20  
  Purchase #4 $134.84   12.220%   $151.3174   $151.32   $151.30   $151.30  
  Purchase #5 $56.47   11.288%   $62.8443   $62.84   $62.85   $62.80  
  Purchase #6 $235.61   5.770%   $249.2047   $249.20   $249.20   $249.20  
  Purchase #7 $135.81   10.541%   $150.1257   $150.13   $150.15   $150.10  
  7 purchase totals = $881.06       $953.9167   $953.91   $953.90   $953.90