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 $217.41   6.688%   $231.9504   $231.95   $231.95   $232.00  
  Purchase #2 $186.67   9.629%   $204.6445   $204.64   $204.65   $204.60  
  Purchase #3 $125.97   4.220%   $131.2859   $131.29   $131.30   $131.30  
  Purchase #4 $186.66   5.150%   $196.273   $196.27   $196.25   $196.30  
  Purchase #5 $89.74   5.809%   $94.953   $94.95   $94.95   $95.00  
  Purchase #6 $90.37   13.672%   $102.7254   $102.73   $102.75   $102.70  
  Purchase #7 $49.90   13.836%   $56.8042   $56.80   $56.80   $56.80  
  7 purchase totals = $946.72       $1,018.6364   $1,018.63   $1,018.65   $1,018.70