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 $55.68   12.507%   $62.6439   $62.64   $62.65   $62.60  
  Purchase #2 $221.53   5.476%   $233.661   $233.66   $233.65   $233.70  
  Purchase #3 $58.31   12.102%   $65.3667   $65.37   $65.35   $65.40  
  Purchase #4 $71.58   7.124%   $76.6794   $76.68   $76.70   $76.70  
  Purchase #5 $159.92   10.234%   $176.2862   $176.29   $176.30   $176.30  
  Purchase #6 $21.55   5.195%   $22.6695   $22.67   $22.65   $22.70  
  Purchase #7 $22.33   10.609%   $24.699   $24.70   $24.70   $24.70  
  7 purchase totals = $610.90       $662.0057   $662.01   $662.00   $662.10