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 $37.79   9.261%   $41.2897   $41.29   $41.30   $41.30  
  Purchase #2 $181.31   13.432%   $205.6636   $205.66   $205.65   $205.70  
  Purchase #3 $162.88   3.452%   $168.5026   $168.50   $168.50   $168.50  
  Purchase #4 $186.36   4.257%   $194.2933   $194.29   $194.30   $194.30  
  Purchase #5 $33.29   3.339%   $34.4016   $34.40   $34.40   $34.40  
  Purchase #6 $87.33   6.807%   $93.2746   $93.27   $93.25   $93.30  
  Purchase #7 $202.92   11.613%   $226.4851   $226.49   $226.50   $226.50  
  7 purchase totals = $891.88       $963.9105   $963.90   $963.90   $964.00