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 $198.52   13.310%   $224.943   $224.94   $224.95   $224.90  
  Purchase #2 $25.71   5.325%   $27.0791   $27.08   $27.10   $27.10  
  Purchase #3 $33.37   6.326%   $35.481   $35.48   $35.50   $35.50  
  Purchase #4 $241.93   8.806%   $263.2344   $263.23   $263.25   $263.20  
  Purchase #5 $182.44   5.762%   $192.9522   $192.95   $192.95   $193.00  
  Purchase #6 $29.80   12.269%   $33.4562   $33.46   $33.45   $33.50  
  Purchase #7 $49.49   11.729%   $55.2947   $55.29   $55.30   $55.30  
  7 purchase totals = $761.26       $832.4406   $832.43   $832.50   $832.50