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 $62.76   3.493%   $64.9522   $64.95   $64.95   $65.00  
  Purchase #2 $148.49   12.257%   $166.6904   $166.69   $166.70   $166.70  
  Purchase #3 $79.58   12.106%   $89.214   $89.21   $89.20   $89.20  
  Purchase #4 $102.67   3.520%   $106.284   $106.28   $106.30   $106.30  
  Purchase #5 $244.98   12.417%   $275.3992   $275.40   $275.40   $275.40  
  Purchase #6 $74.27   10.224%   $81.8634   $81.86   $81.85   $81.90  
  Purchase #7 $41.56   8.628%   $45.1458   $45.15   $45.15   $45.10  
  7 purchase totals = $754.31       $829.5490   $829.54   $829.55   $829.60