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 $55.66   7.368%   $59.761   $59.76   $59.75   $59.80  
  Purchase #2 $194.94   13.742%   $221.7287   $221.73   $221.75   $221.70  
  Purchase #3 $41.53   9.597%   $45.5156   $45.52   $45.50   $45.50  
  Purchase #4 $92.74   12.659%   $104.48   $104.48   $104.50   $104.50  
  Purchase #5 $220.79   6.704%   $235.5918   $235.59   $235.60   $235.60  
  Purchase #6 $133.25   4.171%   $138.8079   $138.81   $138.80   $138.80  
  Purchase #7 $73.79   8.318%   $79.9279   $79.93   $79.95   $79.90  
  7 purchase totals = $812.70       $885.8129   $885.82   $885.85   $885.80