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 $61.66   11.466%   $68.7299   $68.73   $68.75   $68.70  
  Purchase #2 $100.65   9.744%   $110.4573   $110.46   $110.45   $110.50  
  Purchase #3 $215.46   4.130%   $224.3585   $224.36   $224.35   $224.40  
  Purchase #4 $147.95   12.644%   $166.6568   $166.66   $166.65   $166.70  
  Purchase #5 $57.34   5.590%   $60.5453   $60.55   $60.55   $60.50  
  Purchase #6 $18.82   6.411%   $20.0266   $20.03   $20.05   $20.00  
  Purchase #7 $112.60   9.306%   $123.0786   $123.08   $123.10   $123.10  
  7 purchase totals = $714.48       $773.8530   $773.87   $773.90   $773.90