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 $67.64   6.171%   $71.8141   $71.81   $71.80   $71.80  
  Purchase #2 $101.82   6.411%   $108.3477   $108.35   $108.35   $108.30  
  Purchase #3 $94.77   5.835%   $100.2998   $100.30   $100.30   $100.30  
  Purchase #4 $202.67   6.546%   $215.9368   $215.94   $215.95   $215.90  
  Purchase #5 $62.75   5.149%   $65.981   $65.98   $66.00   $66.00  
  Purchase #6 $45.93   4.682%   $48.0804   $48.08   $48.10   $48.10  
  Purchase #7 $180.26   11.649%   $201.2585   $201.26   $201.25   $201.30  
  7 purchase totals = $755.84       $811.7183   $811.72   $811.75   $811.70