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 $68.26   11.827%   $76.3331   $76.33   $76.35   $76.30  
  Purchase #2 $151.73   10.210%   $167.2216   $167.22   $167.20   $167.20  
  Purchase #3 $9.32   5.763%   $9.8571   $9.86   $9.85   $9.90  
  Purchase #4 $62.72   10.427%   $69.2598   $69.26   $69.25   $69.30  
  Purchase #5 $210.64   7.812%   $227.0952   $227.10   $227.10   $227.10  
  Purchase #6 $147.84   13.294%   $167.4938   $167.49   $167.50   $167.50  
  Purchase #7 $109.89   9.161%   $119.957   $119.96   $119.95   $120.00  
  7 purchase totals = $760.40       $837.2176   $837.22   $837.20   $837.30