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 $63.84   7.638%   $68.7161   $68.72   $68.70   $68.70  
  Purchase #2 $232.51   12.621%   $261.8551   $261.86   $261.85   $261.90  
  Purchase #3 $120.90   4.663%   $126.5376   $126.54   $126.55   $126.50  
  Purchase #4 $103.81   7.450%   $111.5438   $111.54   $111.55   $111.50  
  Purchase #5 $151.34   8.695%   $164.499   $164.50   $164.50   $164.50  
  Purchase #6 $195.88   12.766%   $220.886   $220.89   $220.90   $220.90  
  Purchase #7 $84.91   10.667%   $93.9673   $93.97   $93.95   $94.00  
  7 purchase totals = $953.19       $1,048.0049   $1,048.02   $1,048.00   $1,048.00