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 $248.55   10.678%   $275.0902   $275.09   $275.10   $275.10  
  Purchase #2 $91.35   13.665%   $103.833   $103.83   $103.85   $103.80  
  Purchase #3 $123.83   7.629%   $133.277   $133.28   $133.30   $133.30  
  Purchase #4 $233.82   11.436%   $260.5597   $260.56   $260.55   $260.60  
  Purchase #5 $159.64   9.524%   $174.8441   $174.84   $174.85   $174.80  
  Purchase #6 $64.44   11.183%   $71.6463   $71.65   $71.65   $71.60  
  Purchase #7 $204.60   5.752%   $216.3686   $216.37   $216.35   $216.40  
  7 purchase totals = $1,126.23       $1,235.6189   $1,235.62   $1,235.65   $1,235.60