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 $240.25   11.262%   $267.307   $267.31   $267.30   $267.30  
  Purchase #2 $31.99   6.353%   $34.0223   $34.02   $34.00   $34.00  
  Purchase #3 $186.68   9.595%   $204.5919   $204.59   $204.60   $204.60  
  Purchase #4 $68.31   7.350%   $73.3308   $73.33   $73.35   $73.30  
  Purchase #5 $12.32   3.717%   $12.7779   $12.78   $12.80   $12.80  
  Purchase #6 $98.64   12.231%   $110.7047   $110.70   $110.70   $110.70  
  Purchase #7 $63.61   7.128%   $68.1441   $68.14   $68.15   $68.10  
  7 purchase totals = $701.80       $770.8787   $770.87   $770.90   $770.80