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 $162.95   5.104%   $171.267   $171.27   $171.25   $171.30  
  Purchase #2 $245.39   11.660%   $274.0025   $274.00   $274.00   $274.00  
  Purchase #3 $196.49   4.427%   $205.1886   $205.19   $205.20   $205.20  
  Purchase #4 $221.61   6.465%   $235.9371   $235.94   $235.95   $235.90  
  Purchase #5 $202.94   3.342%   $209.7223   $209.72   $209.70   $209.70  
  Purchase #6 $83.58   5.203%   $87.9287   $87.93   $87.95   $87.90  
  Purchase #7 $72.98   5.738%   $77.1676   $77.17   $77.15   $77.20  
  7 purchase totals = $1,185.94       $1,261.2138   $1,261.22   $1,261.20   $1,261.20