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 $92.39   9.861%   $101.5006   $101.50   $101.50   $101.50  
  Purchase #2 $232.28   12.646%   $261.6541   $261.65   $261.65   $261.70  
  Purchase #3 $171.33   6.797%   $182.9753   $182.98   $183.00   $183.00  
  Purchase #4 $22.31   5.556%   $23.5495   $23.55   $23.55   $23.50  
  Purchase #5 $207.32   13.369%   $235.0366   $235.04   $235.05   $235.00  
  Purchase #6 $236.35   8.515%   $256.4752   $256.48   $256.50   $256.50  
  Purchase #7 $170.38   12.373%   $191.4611   $191.46   $191.45   $191.50  
  7 purchase totals = $1,132.36       $1,252.6524   $1,252.66   $1,252.70   $1,252.70