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 $207.86   7.426%   $223.2957   $223.30   $223.30   $223.30  
  Purchase #2 $99.95   3.390%   $103.3383   $103.34   $103.35   $103.30  
  Purchase #3 $66.86   9.684%   $73.3347   $73.33   $73.35   $73.30  
  Purchase #4 $72.58   11.135%   $80.6618   $80.66   $80.65   $80.70  
  Purchase #5 $126.31   5.581%   $133.3594   $133.36   $133.35   $133.40  
  Purchase #6 $192.28   6.585%   $204.9416   $204.94   $204.95   $204.90  
  Purchase #7 $52.35   3.421%   $54.1409   $54.14   $54.15   $54.10  
  7 purchase totals = $818.19       $873.0724   $873.07   $873.10   $873.00