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 $147.82   10.617%   $163.514   $163.51   $163.50   $163.50  
  Purchase #2 $176.44   12.585%   $198.645   $198.65   $198.65   $198.60  
  Purchase #3 $10.73   11.612%   $11.976   $11.98   $12.00   $12.00  
  Purchase #4 $102.35   9.529%   $112.1029   $112.10   $112.10   $112.10  
  Purchase #5 $226.66   3.666%   $234.9694   $234.97   $234.95   $235.00  
  Purchase #6 $138.97   10.826%   $154.0149   $154.01   $154.00   $154.00  
  Purchase #7 $30.97   9.789%   $34.0017   $34.00   $34.00   $34.00  
  7 purchase totals = $833.94       $909.2239   $909.22   $909.20   $909.20