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 $46.88   12.404%   $52.695   $52.70   $52.70   $52.70  
  Purchase #2 $160.55   6.229%   $170.5507   $170.55   $170.55   $170.60  
  Purchase #3 $68.72   6.358%   $73.0892   $73.09   $73.10   $73.10  
  Purchase #4 $210.52   7.359%   $226.0122   $226.01   $226.00   $226.00  
  Purchase #5 $240.43   4.652%   $251.6148   $251.61   $251.60   $251.60  
  Purchase #6 $72.69   6.738%   $77.5879   $77.59   $77.60   $77.60  
  Purchase #7 $110.90   13.555%   $125.9325   $125.93   $125.95   $125.90  
  7 purchase totals = $910.69       $977.4823   $977.48   $977.50   $977.50