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 $93.41   3.787%   $96.9474   $96.95   $96.95   $96.90  
  Purchase #2 $134.52   12.569%   $151.4278   $151.43   $151.45   $151.40  
  Purchase #3 $210.77   10.148%   $232.1589   $232.16   $232.15   $232.20  
  Purchase #4 $74.94   3.393%   $77.4827   $77.48   $77.50   $77.50  
  Purchase #5 $41.32   7.218%   $44.3025   $44.30   $44.30   $44.30  
  Purchase #6 $54.43   5.661%   $57.5113   $57.51   $57.50   $57.50  
  Purchase #7 $210.53   6.328%   $223.8523   $223.85   $223.85   $223.90  
  7 purchase totals = $819.92       $883.6829   $883.68   $883.70   $883.70