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 $217.48   11.129%   $241.6833   $241.68   $241.70   $241.70  
  Purchase #2 $234.80   12.257%   $263.5794   $263.58   $263.60   $263.60  
  Purchase #3 $167.86   5.396%   $176.9177   $176.92   $176.90   $176.90  
  Purchase #4 $106.96   6.679%   $114.1039   $114.10   $114.10   $114.10  
  Purchase #5 $56.50   8.214%   $61.1409   $61.14   $61.15   $61.10  
  Purchase #6 $224.67   8.690%   $244.1938   $244.19   $244.20   $244.20  
  Purchase #7 $149.35   10.437%   $164.9377   $164.94   $164.95   $164.90  
  7 purchase totals = $1,157.62       $1,266.5567   $1,266.55   $1,266.60   $1,266.50