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 $57.34   3.234%   $59.1944   $59.19   $59.20   $59.20  
  Purchase #2 $197.64   6.647%   $210.7771   $210.78   $210.80   $210.80  
  Purchase #3 $170.61   10.836%   $189.0973   $189.10   $189.10   $189.10  
  Purchase #4 $93.43   4.297%   $97.4447   $97.44   $97.45   $97.40  
  Purchase #5 $120.28   3.807%   $124.8591   $124.86   $124.85   $124.90  
  Purchase #6 $186.77   10.564%   $206.5004   $206.50   $206.50   $206.50  
  Purchase #7 $26.38   11.588%   $29.4369   $29.44   $29.45   $29.40  
  7 purchase totals = $852.45       $917.3099   $917.31   $917.35   $917.30