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 $110.90   12.719%   $125.0054   $125.01   $125.00   $125.00  
  Purchase #2 $212.58   9.409%   $232.5817   $232.58   $232.60   $232.60  
  Purchase #3 $94.66   4.456%   $98.878   $98.88   $98.90   $98.90  
  Purchase #4 $212.40   5.234%   $223.517   $223.52   $223.50   $223.50  
  Purchase #5 $64.63   10.348%   $71.3179   $71.32   $71.30   $71.30  
  Purchase #6 $11.33   10.265%   $12.493   $12.49   $12.50   $12.50  
  Purchase #7 $168.72   3.350%   $174.3721   $174.37   $174.35   $174.40  
  7 purchase totals = $875.22       $938.1651   $938.17   $938.15   $938.20