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 $194.44   11.511%   $216.822   $216.82   $216.80   $216.80  
  Purchase #2 $181.69   12.163%   $203.789   $203.79   $203.80   $203.80  
  Purchase #3 $250.74   9.319%   $274.1065   $274.11   $274.10   $274.10  
  Purchase #4 $170.48   4.564%   $178.2607   $178.26   $178.25   $178.30  
  Purchase #5 $23.67   9.236%   $25.8562   $25.86   $25.85   $25.90  
  Purchase #6 $241.29   3.444%   $249.6   $249.60   $249.60   $249.60  
  Purchase #7 $19.54   7.310%   $20.9684   $20.97   $20.95   $21.00  
  7 purchase totals = $1,081.85       $1,169.4028   $1,169.41   $1,169.35   $1,169.50