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 $126.69   11.844%   $141.6952   $141.70   $141.70   $141.70  
  Purchase #2 $88.85   10.677%   $98.3365   $98.34   $98.35   $98.30  
  Purchase #3 $8.66   11.316%   $9.64   $9.64   $9.65   $9.60  
  Purchase #4 $223.92   12.527%   $251.9705   $251.97   $251.95   $252.00  
  Purchase #5 $160.86   12.582%   $181.0994   $181.10   $181.10   $181.10  
  Purchase #6 $234.61   13.575%   $266.4583   $266.46   $266.45   $266.50  
  Purchase #7 $7.44   11.638%   $8.3059   $8.31   $8.30   $8.30  
  7 purchase totals = $851.03       $957.5058   $957.52   $957.50   $957.50