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 $165.76   11.629%   $185.0362   $185.04   $185.05   $185.00  
  Purchase #2 $205.67   13.645%   $233.7337   $233.73   $233.75   $233.70  
  Purchase #3 $6.30   9.768%   $6.9154   $6.92   $6.90   $6.90  
  Purchase #4 $67.98   7.693%   $73.2097   $73.21   $73.20   $73.20  
  Purchase #5 $154.80   11.232%   $172.1871   $172.19   $172.20   $172.20  
  Purchase #6 $58.25   9.271%   $63.6504   $63.65   $63.65   $63.70  
  Purchase #7 $125.31   10.327%   $138.2508   $138.25   $138.25   $138.30  
  7 purchase totals = $784.07       $872.9833   $872.99   $873.00   $873.00