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 $163.70   12.164%   $183.6125   $183.61   $183.60   $183.60  
  Purchase #2 $51.25   11.143%   $56.9608   $56.96   $56.95   $57.00  
  Purchase #3 $55.98   3.867%   $58.1447   $58.14   $58.15   $58.10  
  Purchase #4 $111.45   6.472%   $118.663   $118.66   $118.65   $118.70  
  Purchase #5 $242.98   3.277%   $250.9425   $250.94   $250.95   $250.90  
  Purchase #6 $182.86   11.488%   $203.867   $203.87   $203.85   $203.90  
  Purchase #7 $152.85   10.606%   $169.0613   $169.06   $169.05   $169.10  
  7 purchase totals = $961.07       $1,041.2518   $1,041.24   $1,041.20   $1,041.30