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 $47.94   10.505%   $52.9761   $52.98   $53.00   $53.00  
  Purchase #2 $184.28   7.407%   $197.9296   $197.93   $197.95   $197.90  
  Purchase #3 $178.53   6.817%   $190.7004   $190.70   $190.70   $190.70  
  Purchase #4 $93.93   13.191%   $106.3203   $106.32   $106.30   $106.30  
  Purchase #5 $71.91   3.427%   $74.3744   $74.37   $74.35   $74.40  
  Purchase #6 $113.73   11.494%   $126.8021   $126.80   $126.80   $126.80  
  Purchase #7 $108.88   6.265%   $115.7013   $115.70   $115.70   $115.70  
  7 purchase totals = $799.20       $864.8042   $864.80   $864.80   $864.80