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 $67.48   10.352%   $74.4655   $74.47   $74.45   $74.50  
  Purchase #2 $53.33   5.641%   $56.3383   $56.34   $56.35   $56.30  
  Purchase #3 $89.85   6.756%   $95.9203   $95.92   $95.90   $95.90  
  Purchase #4 $246.78   10.589%   $272.9115   $272.91   $272.90   $272.90  
  Purchase #5 $177.26   4.357%   $184.9832   $184.98   $185.00   $185.00  
  Purchase #6 $217.92   7.381%   $234.0047   $234.00   $234.00   $234.00  
  Purchase #7 $86.72   5.117%   $91.1575   $91.16   $91.15   $91.20  
  7 purchase totals = $939.34       $1,009.7810   $1,009.78   $1,009.75   $1,009.80