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 $22.52   8.716%   $24.4828   $24.48   $24.50   $24.50  
  Purchase #2 $209.81   13.362%   $237.8448   $237.84   $237.85   $237.80  
  Purchase #3 $244.98   4.809%   $256.7611   $256.76   $256.75   $256.80  
  Purchase #4 $17.31   3.666%   $17.9446   $17.94   $17.95   $17.90  
  Purchase #5 $173.71   13.582%   $197.3033   $197.30   $197.30   $197.30  
  Purchase #6 $84.97   7.728%   $91.5365   $91.54   $91.55   $91.50  
  Purchase #7 $226.44   3.120%   $233.5049   $233.50   $233.50   $233.50  
  7 purchase totals = $979.74       $1,059.3780   $1,059.36   $1,059.40   $1,059.30