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 $244.26   6.252%   $259.5311   $259.53   $259.55   $259.50  
  Purchase #2 $238.72   9.563%   $261.5488   $261.55   $261.55   $261.50  
  Purchase #3 $124.98   6.711%   $133.3674   $133.37   $133.35   $133.40  
  Purchase #4 $52.28   11.656%   $58.3738   $58.37   $58.35   $58.40  
  Purchase #5 $206.50   13.701%   $234.7926   $234.79   $234.80   $234.80  
  Purchase #6 $11.37   9.792%   $12.4834   $12.48   $12.50   $12.50  
  Purchase #7 $72.75   13.413%   $82.508   $82.51   $82.50   $82.50  
  7 purchase totals = $950.86       $1,042.6051   $1,042.60   $1,042.60   $1,042.60