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 $58.84   12.672%   $66.2962   $66.30   $66.30   $66.30  
  Purchase #2 $177.37   13.363%   $201.072   $201.07   $201.05   $201.10  
  Purchase #3 $82.37   3.591%   $85.3279   $85.33   $85.35   $85.30  
  Purchase #4 $150.68   8.201%   $163.0373   $163.04   $163.05   $163.00  
  Purchase #5 $65.87   8.826%   $71.6837   $71.68   $71.70   $71.70  
  Purchase #6 $182.61   13.826%   $207.8577   $207.86   $207.85   $207.90  
  Purchase #7 $32.55   8.254%   $35.2367   $35.24   $35.25   $35.20  
  7 purchase totals = $750.29       $830.5115   $830.52   $830.55   $830.50