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 $59.95   8.675%   $65.1507   $65.15   $65.15   $65.20  
  Purchase #2 $120.62   11.259%   $134.2006   $134.20   $134.20   $134.20  
  Purchase #3 $91.75   6.171%   $97.4119   $97.41   $97.40   $97.40  
  Purchase #4 $178.91   13.535%   $203.1255   $203.13   $203.15   $203.10  
  Purchase #5 $202.64   6.402%   $215.613   $215.61   $215.60   $215.60  
  Purchase #6 $50.49   3.564%   $52.2895   $52.29   $52.30   $52.30  
  Purchase #7 $146.74   9.363%   $160.4793   $160.48   $160.50   $160.50  
  7 purchase totals = $851.10       $928.2705   $928.27   $928.30   $928.30