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 $57.80   8.779%   $62.8743   $62.87   $62.85   $62.90  
  Purchase #2 $212.82   9.799%   $233.6742   $233.67   $233.65   $233.70  
  Purchase #3 $154.47   6.818%   $165.0018   $165.00   $165.00   $165.00  
  Purchase #4 $193.44   12.308%   $217.2486   $217.25   $217.25   $217.20  
  Purchase #5 $91.31   12.777%   $102.9767   $102.98   $103.00   $103.00  
  Purchase #6 $94.34   5.542%   $99.5683   $99.57   $99.55   $99.60  
  Purchase #7 $23.48   7.711%   $25.2905   $25.29   $25.30   $25.30  
  7 purchase totals = $827.66       $906.6344   $906.63   $906.60   $906.70