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 $58.79   10.474%   $64.9477   $64.95   $64.95   $64.90  
  Purchase #2 $86.46   9.203%   $94.4169   $94.42   $94.40   $94.40  
  Purchase #3 $160.33   9.418%   $175.4299   $175.43   $175.45   $175.40  
  Purchase #4 $233.27   5.166%   $245.3207   $245.32   $245.30   $245.30  
  Purchase #5 $179.62   8.103%   $194.1746   $194.17   $194.15   $194.20  
  Purchase #6 $234.88   12.285%   $263.735   $263.74   $263.75   $263.70  
  Purchase #7 $151.38   9.553%   $165.8413   $165.84   $165.85   $165.80  
  7 purchase totals = $1,104.73       $1,203.8661   $1,203.87   $1,203.85   $1,203.70