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 $195.44   6.217%   $207.5905   $207.59   $207.60   $207.60  
  Purchase #2 $159.35   5.441%   $168.0202   $168.02   $168.00   $168.00  
  Purchase #3 $191.65   11.139%   $212.9979   $213.00   $213.00   $213.00  
  Purchase #4 $245.92   3.833%   $255.3461   $255.35   $255.35   $255.30  
  Purchase #5 $124.34   9.438%   $136.0752   $136.08   $136.10   $136.10  
  Purchase #6 $226.52   3.166%   $233.6916   $233.69   $233.70   $233.70  
  Purchase #7 $217.75   9.522%   $238.4842   $238.48   $238.50   $238.50  
  7 purchase totals = $1,360.97       $1,452.2057   $1,452.21   $1,452.25   $1,452.20