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 $47.39   6.740%   $50.5841   $50.58   $50.60   $50.60  
  Purchase #2 $220.96   10.328%   $243.7807   $243.78   $243.80   $243.80  
  Purchase #3 $71.73   11.227%   $79.7831   $79.78   $79.80   $79.80  
  Purchase #4 $71.91   12.752%   $81.08   $81.08   $81.10   $81.10  
  Purchase #5 $56.81   4.695%   $59.4772   $59.48   $59.50   $59.50  
  Purchase #6 $225.41   11.590%   $251.535   $251.54   $251.55   $251.50  
  Purchase #7 $140.87   12.755%   $158.838   $158.84   $158.85   $158.80  
  7 purchase totals = $835.08       $925.0781   $925.08   $925.20   $925.10