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 $230.25   11.405%   $256.51   $256.51   $256.50   $256.50  
  Purchase #2 $131.27   4.548%   $137.2402   $137.24   $137.25   $137.20  
  Purchase #3 $172.82   3.809%   $179.4027   $179.40   $179.40   $179.40  
  Purchase #4 $189.98   9.579%   $208.1782   $208.18   $208.20   $208.20  
  Purchase #5 $180.64   7.376%   $193.964   $193.96   $193.95   $194.00  
  Purchase #6 $224.37   9.866%   $246.5063   $246.51   $246.50   $246.50  
  Purchase #7 $29.58   9.588%   $32.4161   $32.42   $32.40   $32.40  
  7 purchase totals = $1,158.91       $1,254.2175   $1,254.22   $1,254.20   $1,254.20