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 $61.25   5.633%   $64.7002   $64.70   $64.70   $64.70  
  Purchase #2 $105.92   10.306%   $116.8361   $116.84   $116.85   $116.80  
  Purchase #3 $165.43   12.464%   $186.0492   $186.05   $186.05   $186.00  
  Purchase #4 $89.89   6.571%   $95.7967   $95.80   $95.80   $95.80  
  Purchase #5 $51.74   6.463%   $55.084   $55.08   $55.10   $55.10  
  Purchase #6 $246.94   5.564%   $260.6797   $260.68   $260.70   $260.70  
  Purchase #7 $75.66   12.707%   $85.2741   $85.27   $85.25   $85.30  
  7 purchase totals = $796.83       $864.4200   $864.42   $864.45   $864.40