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 $233.47   4.102%   $243.0469   $243.05   $243.05   $243.00  
  Purchase #2 $6.36   3.370%   $6.5743   $6.57   $6.55   $6.60  
  Purchase #3 $123.48   6.847%   $131.9347   $131.93   $131.95   $131.90  
  Purchase #4 $113.42   5.722%   $119.9099   $119.91   $119.90   $119.90  
  Purchase #5 $216.31   11.711%   $241.6421   $241.64   $241.65   $241.60  
  Purchase #6 $205.94   8.319%   $223.0721   $223.07   $223.05   $223.10  
  Purchase #7 $45.35   4.737%   $47.4982   $47.50   $47.50   $47.50  
  7 purchase totals = $944.33       $1,013.6782   $1,013.67   $1,013.65   $1,013.60