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 $216.87   5.241%   $228.2362   $228.24   $228.25   $228.20  
  Purchase #2 $186.43   9.365%   $203.8892   $203.89   $203.90   $203.90  
  Purchase #3 $126.38   5.440%   $133.2551   $133.26   $133.25   $133.30  
  Purchase #4 $210.84   8.102%   $227.9223   $227.92   $227.90   $227.90  
  Purchase #5 $58.96   7.405%   $63.326   $63.33   $63.35   $63.30  
  Purchase #6 $156.96   5.520%   $165.6242   $165.62   $165.60   $165.60  
  Purchase #7 $228.53   4.399%   $238.583   $238.58   $238.60   $238.60  
  7 purchase totals = $1,184.97       $1,260.8360   $1,260.84   $1,260.85   $1,260.80