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 $234.29   8.740%   $254.7669   $254.77   $254.75   $254.80  
  Purchase #2 $244.47   12.262%   $274.4469   $274.45   $274.45   $274.40  
  Purchase #3 $133.43   7.790%   $143.8242   $143.82   $143.80   $143.80  
  Purchase #4 $233.48   6.162%   $247.867   $247.87   $247.85   $247.90  
  Purchase #5 $101.27   6.391%   $107.7422   $107.74   $107.75   $107.70  
  Purchase #6 $166.54   4.727%   $174.4123   $174.41   $174.40   $174.40  
  Purchase #7 $133.34   7.758%   $143.6845   $143.68   $143.70   $143.70  
  7 purchase totals = $1,246.82       $1,346.7440   $1,346.74   $1,346.70   $1,346.70