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 $150.99   10.158%   $166.3276   $166.33   $166.35   $166.30  
  Purchase #2 $99.79   4.154%   $103.9353   $103.94   $103.95   $103.90  
  Purchase #3 $78.46   5.453%   $82.7384   $82.74   $82.75   $82.70  
  Purchase #4 $36.44   5.215%   $38.3403   $38.34   $38.35   $38.30  
  Purchase #5 $160.60   11.126%   $178.4684   $178.47   $178.45   $178.50  
  Purchase #6 $46.45   11.612%   $51.8438   $51.84   $51.85   $51.80  
  Purchase #7 $195.87   3.208%   $202.1535   $202.15   $202.15   $202.20  
  7 purchase totals = $768.60       $823.8073   $823.81   $823.85   $823.70