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 $204.82   10.354%   $226.0271   $226.03   $226.05   $226.00  
  Purchase #2 $45.31   10.390%   $50.0177   $50.02   $50.00   $50.00  
  Purchase #3 $58.94   10.219%   $64.9631   $64.96   $64.95   $65.00  
  Purchase #4 $163.82   9.570%   $179.4976   $179.50   $179.50   $179.50  
  Purchase #5 $163.82   9.281%   $179.0241   $179.02   $179.00   $179.00  
  Purchase #6 $178.81   9.600%   $195.9758   $195.98   $196.00   $196.00  
  Purchase #7 $192.38   8.827%   $209.3614   $209.36   $209.35   $209.40  
  7 purchase totals = $1,007.90       $1,104.8668   $1,104.87   $1,104.85   $1,104.90