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 $198.68   6.862%   $212.3134   $212.31   $212.30   $212.30  
  Purchase #2 $61.37   4.692%   $64.2495   $64.25   $64.25   $64.20  
  Purchase #3 $20.63   11.220%   $22.9447   $22.94   $22.95   $22.90  
  Purchase #4 $172.25   3.484%   $178.2512   $178.25   $178.25   $178.30  
  Purchase #5 $248.67   4.111%   $258.8928   $258.89   $258.90   $258.90  
  Purchase #6 $172.33   5.342%   $181.5359   $181.54   $181.55   $181.50  
  Purchase #7 $39.94   9.686%   $43.8086   $43.81   $43.80   $43.80  
  7 purchase totals = $913.87       $961.9961   $961.99   $962.00   $961.90