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 $98.53   4.552%   $103.0151   $103.02   $103.00   $103.00  
  Purchase #2 $240.29   9.723%   $263.6534   $263.65   $263.65   $263.70  
  Purchase #3 $235.48   4.507%   $246.0931   $246.09   $246.10   $246.10  
  Purchase #4 $147.96   13.605%   $168.09   $168.09   $168.10   $168.10  
  Purchase #5 $116.95   13.437%   $132.6646   $132.66   $132.65   $132.70  
  Purchase #6 $180.90   8.463%   $196.2096   $196.21   $196.20   $196.20  
  Purchase #7 $125.78   12.795%   $141.8736   $141.87   $141.85   $141.90  
  7 purchase totals = $1,145.89       $1,251.5994   $1,251.59   $1,251.55   $1,251.70