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 $58.91   10.428%   $65.0531   $65.05   $65.05   $65.10  
  Purchase #2 $28.52   6.349%   $30.3307   $30.33   $30.35   $30.30  
  Purchase #3 $23.36   13.706%   $26.5617   $26.56   $26.55   $26.60  
  Purchase #4 $250.46   3.607%   $259.4941   $259.49   $259.50   $259.50  
  Purchase #5 $148.93   12.785%   $167.9707   $167.97   $167.95   $168.00  
  Purchase #6 $221.66   4.805%   $232.3108   $232.31   $232.30   $232.30  
  Purchase #7 $207.66   12.548%   $233.7172   $233.72   $233.70   $233.70  
  7 purchase totals = $939.50       $1,015.4383   $1,015.43   $1,015.40   $1,015.50