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 $203.52   5.571%   $214.8581   $214.86   $214.85   $214.90  
  Purchase #2 $185.83   8.307%   $201.2669   $201.27   $201.25   $201.30  
  Purchase #3 $182.50   13.424%   $206.9988   $207.00   $207.00   $207.00  
  Purchase #4 $88.93   6.254%   $94.4917   $94.49   $94.50   $94.50  
  Purchase #5 $227.65   4.866%   $238.7274   $238.73   $238.75   $238.70  
  Purchase #6 $133.62   3.665%   $138.5172   $138.52   $138.50   $138.50  
  Purchase #7 $158.94   6.276%   $168.9151   $168.92   $168.90   $168.90  
  7 purchase totals = $1,180.99       $1,263.7752   $1,263.79   $1,263.75   $1,263.80