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 $201.27   5.576%   $212.4928   $212.49   $212.50   $212.50  
  Purchase #2 $242.84   6.344%   $258.2458   $258.25   $258.25   $258.20  
  Purchase #3 $187.39   3.563%   $194.0667   $194.07   $194.05   $194.10  
  Purchase #4 $101.82   4.672%   $106.577   $106.58   $106.60   $106.60  
  Purchase #5 $45.25   13.608%   $51.4076   $51.41   $51.40   $51.40  
  Purchase #6 $38.78   12.135%   $43.486   $43.49   $43.50   $43.50  
  Purchase #7 $140.93   10.692%   $155.9982   $156.00   $156.00   $156.00  
  7 purchase totals = $958.28       $1,022.2741   $1,022.29   $1,022.30   $1,022.30