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 $232.93   12.578%   $262.2279   $262.23   $262.25   $262.20  
  Purchase #2 $29.97   6.401%   $31.8884   $31.89   $31.90   $31.90  
  Purchase #3 $22.57   4.206%   $23.5193   $23.52   $23.50   $23.50  
  Purchase #4 $76.97   13.865%   $87.6419   $87.64   $87.65   $87.60  
  Purchase #5 $238.98   12.779%   $269.5193   $269.52   $269.50   $269.50  
  Purchase #6 $132.73   5.301%   $139.766   $139.77   $139.75   $139.80  
  Purchase #7 $96.71   6.505%   $103.001   $103.00   $103.00   $103.00  
  7 purchase totals = $830.86       $917.5638   $917.57   $917.55   $917.50