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 $61.96   4.301%   $64.6249   $64.62   $64.60   $64.60  
  Purchase #2 $180.25   9.167%   $196.7735   $196.77   $196.75   $196.80  
  Purchase #3 $24.38   8.471%   $26.4452   $26.45   $26.45   $26.40  
  Purchase #4 $237.80   12.203%   $266.8187   $266.82   $266.80   $266.80  
  Purchase #5 $148.95   11.305%   $165.7888   $165.79   $165.80   $165.80  
  Purchase #6 $65.74   6.494%   $70.0092   $70.01   $70.00   $70.00  
  Purchase #7 $128.79   13.846%   $146.6223   $146.62   $146.60   $146.60  
  7 purchase totals = $847.87       $937.0826   $937.08   $937.00   $937.00