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 $224.74   9.786%   $246.7331   $246.73   $246.75   $246.70  
  Purchase #2 $83.37   4.265%   $86.9257   $86.93   $86.95   $86.90  
  Purchase #3 $25.52   12.349%   $28.6715   $28.67   $28.65   $28.70  
  Purchase #4 $46.69   4.522%   $48.8013   $48.80   $48.80   $48.80  
  Purchase #5 $201.35   3.139%   $207.6704   $207.67   $207.65   $207.70  
  Purchase #6 $109.83   13.824%   $125.0129   $125.01   $125.00   $125.00  
  Purchase #7 $191.27   5.137%   $201.0955   $201.10   $201.10   $201.10  
  7 purchase totals = $882.77       $944.9104   $944.91   $944.90   $944.90