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 $199.94   6.286%   $212.5082   $212.51   $212.50   $212.50  
  Purchase #2 $122.92   10.804%   $136.2003   $136.20   $136.20   $136.20  
  Purchase #3 $64.45   3.173%   $66.495   $66.50   $66.50   $66.50  
  Purchase #4 $244.85   8.711%   $266.1789   $266.18   $266.20   $266.20  
  Purchase #5 $181.41   12.654%   $204.3656   $204.37   $204.35   $204.40  
  Purchase #6 $23.48   3.156%   $24.221   $24.22   $24.20   $24.20  
  Purchase #7 $122.68   7.414%   $131.7755   $131.78   $131.80   $131.80  
  7 purchase totals = $959.73       $1,041.7445   $1,041.76   $1,041.75   $1,041.80