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 $22.73   3.476%   $23.5201   $23.52   $23.50   $23.50  
  Purchase #2 $241.63   8.568%   $262.3329   $262.33   $262.35   $262.30  
  Purchase #3 $192.41   11.146%   $213.856   $213.86   $213.85   $213.90  
  Purchase #4 $235.71   10.667%   $260.8532   $260.85   $260.85   $260.90  
  Purchase #5 $65.71   7.159%   $70.4142   $70.41   $70.40   $70.40  
  Purchase #6 $204.88   13.830%   $233.2149   $233.21   $233.20   $233.20  
  Purchase #7 $165.78   9.251%   $181.1163   $181.12   $181.10   $181.10  
  7 purchase totals = $1,128.85       $1,245.3076   $1,245.30   $1,245.25   $1,245.30