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 $56.85   6.398%   $60.4873   $60.49   $60.50   $60.50  
  Purchase #2 $50.93   7.514%   $54.7569   $54.76   $54.75   $54.80  
  Purchase #3 $242.42   6.732%   $258.7397   $258.74   $258.75   $258.70  
  Purchase #4 $233.26   4.385%   $243.4885   $243.49   $243.50   $243.50  
  Purchase #5 $113.84   4.178%   $118.5962   $118.60   $118.60   $118.60  
  Purchase #6 $238.70   6.798%   $254.9268   $254.93   $254.95   $254.90  
  Purchase #7 $170.33   7.694%   $183.4352   $183.44   $183.45   $183.40  
  7 purchase totals = $1,106.33       $1,174.4306   $1,174.45   $1,174.50   $1,174.40