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 $92.44   11.267%   $102.8552   $102.86   $102.85   $102.90  
  Purchase #2 $219.62   11.392%   $244.6391   $244.64   $244.65   $244.60  
  Purchase #3 $107.77   9.371%   $117.8691   $117.87   $117.85   $117.90  
  Purchase #4 $142.51   8.434%   $154.5293   $154.53   $154.55   $154.50  
  Purchase #5 $229.70   13.203%   $260.0273   $260.03   $260.05   $260.00  
  Purchase #6 $168.31   12.110%   $188.6923   $188.69   $188.70   $188.70  
  Purchase #7 $27.52   7.187%   $29.4979   $29.50   $29.50   $29.50  
  7 purchase totals = $987.87       $1,098.1102   $1,098.12   $1,098.15   $1,098.10