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 $71.41   6.586%   $76.1131   $76.11   $76.10   $76.10  
  Purchase #2 $195.37   12.496%   $219.7834   $219.78   $219.80   $219.80  
  Purchase #3 $145.95   7.539%   $156.9532   $156.95   $156.95   $157.00  
  Purchase #4 $107.47   13.125%   $121.5754   $121.58   $121.60   $121.60  
  Purchase #5 $109.28   11.312%   $121.6418   $121.64   $121.65   $121.60  
  Purchase #6 $118.99   11.310%   $132.4478   $132.45   $132.45   $132.40  
  Purchase #7 $66.27   7.855%   $71.4755   $71.48   $71.50   $71.50  
  7 purchase totals = $814.74       $899.9902   $899.99   $900.05   $900.00