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 $199.59   10.707%   $220.9601   $220.96   $220.95   $221.00  
  Purchase #2 $119.93   3.689%   $124.3542   $124.35   $124.35   $124.40  
  Purchase #3 $155.89   11.697%   $174.1245   $174.12   $174.10   $174.10  
  Purchase #4 $167.78   4.771%   $175.7848   $175.78   $175.80   $175.80  
  Purchase #5 $195.27   12.154%   $219.0031   $219.00   $219.00   $219.00  
  Purchase #6 $58.63   7.154%   $62.8244   $62.82   $62.80   $62.80  
  Purchase #7 $217.28   7.527%   $233.6347   $233.63   $233.65   $233.60  
  7 purchase totals = $1,114.37       $1,210.6858   $1,210.66   $1,210.65   $1,210.70