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 $181.43   5.757%   $191.8749   $191.87   $191.85   $191.90  
  Purchase #2 $9.39   5.581%   $9.9141   $9.91   $9.90   $9.90  
  Purchase #3 $78.40   3.826%   $81.3996   $81.40   $81.40   $81.40  
  Purchase #4 $141.31   9.584%   $154.8532   $154.85   $154.85   $154.90  
  Purchase #5 $68.73   12.217%   $77.1267   $77.13   $77.15   $77.10  
  Purchase #6 $22.88   9.185%   $24.9815   $24.98   $25.00   $25.00  
  Purchase #7 $11.67   7.180%   $12.5079   $12.51   $12.50   $12.50  
  7 purchase totals = $513.81       $552.6579   $552.65   $552.65   $552.70