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 $216.92   12.484%   $244.0003   $244.00   $244.00   $244.00  
  Purchase #2 $243.28   4.116%   $253.2934   $253.29   $253.30   $253.30  
  Purchase #3 $93.74   7.257%   $100.5427   $100.54   $100.55   $100.50  
  Purchase #4 $39.67   13.334%   $44.9596   $44.96   $44.95   $45.00  
  Purchase #5 $174.48   11.873%   $195.196   $195.20   $195.20   $195.20  
  Purchase #6 $26.81   6.186%   $28.4685   $28.47   $28.45   $28.50  
  Purchase #7 $87.96   9.546%   $96.3567   $96.36   $96.35   $96.40  
  7 purchase totals = $882.86       $962.8172   $962.82   $962.80   $962.90