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 $197.57   10.652%   $218.6152   $218.62   $218.60   $218.60  
  Purchase #2 $71.82   9.585%   $78.7039   $78.70   $78.70   $78.70  
  Purchase #3 $43.41   6.869%   $46.3918   $46.39   $46.40   $46.40  
  Purchase #4 $242.62   12.475%   $272.8868   $272.89   $272.90   $272.90  
  Purchase #5 $159.68   13.681%   $181.5258   $181.53   $181.55   $181.50  
  Purchase #6 $101.44   9.385%   $110.9601   $110.96   $110.95   $111.00  
  Purchase #7 $49.92   5.531%   $52.6811   $52.68   $52.70   $52.70  
  7 purchase totals = $866.46       $961.7647   $961.77   $961.80   $961.80