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 $208.26   6.121%   $221.0076   $221.01   $221.00   $221.00  
  Purchase #2 $104.68   6.837%   $111.837   $111.84   $111.85   $111.80  
  Purchase #3 $228.53   8.211%   $247.2946   $247.29   $247.30   $247.30  
  Purchase #4 $137.75   11.133%   $153.0857   $153.09   $153.10   $153.10  
  Purchase #5 $93.38   9.691%   $102.4295   $102.43   $102.45   $102.40  
  Purchase #6 $24.66   5.456%   $26.0054   $26.01   $26.00   $26.00  
  Purchase #7 $214.39   9.135%   $233.9745   $233.97   $233.95   $234.00  
  7 purchase totals = $1,011.65       $1,095.6343   $1,095.64   $1,095.65   $1,095.60