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 $102.47   6.559%   $109.191   $109.19   $109.20   $109.20  
  Purchase #2 $82.94   3.234%   $85.6223   $85.62   $85.60   $85.60  
  Purchase #3 $200.26   6.275%   $212.8263   $212.83   $212.85   $212.80  
  Purchase #4 $236.71   4.273%   $246.8246   $246.82   $246.80   $246.80  
  Purchase #5 $48.47   8.467%   $52.574   $52.57   $52.55   $52.60  
  Purchase #6 $200.99   7.548%   $216.1607   $216.16   $216.15   $216.20  
  Purchase #7 $113.66   3.480%   $117.6154   $117.62   $117.60   $117.60  
  7 purchase totals = $985.50       $1,040.8143   $1,040.81   $1,040.75   $1,040.80