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 $111.53   7.570%   $119.9728   $119.97   $119.95   $120.00  
  Purchase #2 $213.48   7.120%   $228.6798   $228.68   $228.70   $228.70  
  Purchase #3 $89.67   9.720%   $98.3859   $98.39   $98.40   $98.40  
  Purchase #4 $183.76   5.446%   $193.7676   $193.77   $193.75   $193.80  
  Purchase #5 $150.53   9.395%   $164.6723   $164.67   $164.65   $164.70  
  Purchase #6 $217.75   6.769%   $232.4895   $232.49   $232.50   $232.50  
  Purchase #7 $14.83   13.412%   $16.819   $16.82   $16.80   $16.80  
  7 purchase totals = $981.55       $1,054.7869   $1,054.79   $1,054.75   $1,054.90