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 $23.57   13.479%   $26.747   $26.75   $26.75   $26.70  
  Purchase #2 $180.57   13.747%   $205.393   $205.39   $205.40   $205.40  
  Purchase #3 $131.26   13.575%   $149.0785   $149.08   $149.10   $149.10  
  Purchase #4 $90.91   4.227%   $94.7528   $94.75   $94.75   $94.80  
  Purchase #5 $200.60   11.867%   $224.4052   $224.41   $224.40   $224.40  
  Purchase #6 $136.42   6.763%   $145.6461   $145.65   $145.65   $145.60  
  Purchase #7 $38.58   3.138%   $39.7906   $39.79   $39.80   $39.80  
  7 purchase totals = $801.91       $885.8132   $885.82   $885.85   $885.80