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 $103.36   8.492%   $112.1373   $112.14   $112.15   $112.10  
  Purchase #2 $26.69   3.739%   $27.6879   $27.69   $27.70   $27.70  
  Purchase #3 $98.70   12.202%   $110.7434   $110.74   $110.75   $110.70  
  Purchase #4 $181.32   6.717%   $193.4993   $193.50   $193.50   $193.50  
  Purchase #5 $243.43   12.575%   $274.0413   $274.04   $274.05   $274.00  
  Purchase #6 $230.63   8.589%   $250.4388   $250.44   $250.45   $250.40  
  Purchase #7 $83.77   3.361%   $86.5855   $86.59   $86.60   $86.60  
  7 purchase totals = $967.90       $1,055.1335   $1,055.14   $1,055.20   $1,055.00