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 $174.49   13.477%   $198.006   $198.01   $198.00   $198.00  
  Purchase #2 $45.68   13.298%   $51.7545   $51.75   $51.75   $51.80  
  Purchase #3 $95.95   11.576%   $107.0572   $107.06   $107.05   $107.10  
  Purchase #4 $176.40   5.427%   $185.9732   $185.97   $185.95   $186.00  
  Purchase #5 $144.47   4.174%   $150.5002   $150.50   $150.50   $150.50  
  Purchase #6 $19.52   3.767%   $20.2553   $20.26   $20.25   $20.30  
  Purchase #7 $49.61   6.528%   $52.8485   $52.85   $52.85   $52.80  
  7 purchase totals = $706.12       $766.3949   $766.40   $766.35   $766.50