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 $58.41   12.446%   $65.6797   $65.68   $65.70   $65.70  
  Purchase #2 $50.39   5.277%   $53.0491   $53.05   $53.05   $53.00  
  Purchase #3 $37.86   13.620%   $43.0165   $43.02   $43.00   $43.00  
  Purchase #4 $168.40   12.801%   $189.9569   $189.96   $189.95   $190.00  
  Purchase #5 $237.96   6.825%   $254.2008   $254.20   $254.20   $254.20  
  Purchase #6 $120.63   7.248%   $129.3733   $129.37   $129.35   $129.40  
  Purchase #7 $125.65   8.564%   $136.4107   $136.41   $136.40   $136.40  
  7 purchase totals = $799.30       $871.6870   $871.69   $871.65   $871.70