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 $248.30   5.647%   $262.3215   $262.32   $262.30   $262.30  
  Purchase #2 $243.31   5.497%   $256.6848   $256.68   $256.70   $256.70  
  Purchase #3 $44.59   4.566%   $46.626   $46.63   $46.65   $46.60  
  Purchase #4 $214.56   12.174%   $240.6805   $240.68   $240.70   $240.70  
  Purchase #5 $235.31   11.599%   $262.6036   $262.60   $262.60   $262.60  
  Purchase #6 $55.71   9.263%   $60.8704   $60.87   $60.85   $60.90  
  Purchase #7 $128.72   10.575%   $142.3321   $142.33   $142.35   $142.30  
  7 purchase totals = $1,170.50       $1,272.1189   $1,272.11   $1,272.15   $1,272.10