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 $161.77   5.727%   $171.0346   $171.03   $171.05   $171.00  
  Purchase #2 $194.64   4.543%   $203.4825   $203.48   $203.50   $203.50  
  Purchase #3 $226.29   13.217%   $256.1987   $256.20   $256.20   $256.20  
  Purchase #4 $58.36   7.481%   $62.7259   $62.73   $62.75   $62.70  
  Purchase #5 $62.93   9.831%   $69.1166   $69.12   $69.10   $69.10  
  Purchase #6 $65.66   12.129%   $73.6239   $73.62   $73.60   $73.60  
  Purchase #7 $225.48   3.695%   $233.8115   $233.81   $233.80   $233.80  
  7 purchase totals = $995.13       $1,069.9937   $1,069.99   $1,070.00   $1,069.90