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 $193.47   5.856%   $204.7996   $204.80   $204.80   $204.80  
  Purchase #2 $240.61   11.116%   $267.3562   $267.36   $267.35   $267.40  
  Purchase #3 $135.68   6.545%   $144.5603   $144.56   $144.55   $144.60  
  Purchase #4 $179.25   8.220%   $193.9844   $193.98   $194.00   $194.00  
  Purchase #5 $213.55   13.457%   $242.2874   $242.29   $242.30   $242.30  
  Purchase #6 $101.39   6.142%   $107.6174   $107.62   $107.60   $107.60  
  Purchase #7 $167.66   5.569%   $176.997   $177.00   $177.00   $177.00  
  7 purchase totals = $1,231.61       $1,337.6023   $1,337.61   $1,337.60   $1,337.70