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 $207.90   10.646%   $230.033   $230.03   $230.05   $230.00  
  Purchase #2 $110.45   13.493%   $125.353   $125.35   $125.35   $125.40  
  Purchase #3 $163.62   6.630%   $174.468   $174.47   $174.45   $174.50  
  Purchase #4 $60.33   9.222%   $65.8936   $65.89   $65.90   $65.90  
  Purchase #5 $139.58   12.192%   $156.5976   $156.60   $156.60   $156.60  
  Purchase #6 $217.94   11.854%   $243.7746   $243.77   $243.75   $243.80  
  Purchase #7 $45.33   4.170%   $47.2203   $47.22   $47.20   $47.20  
  7 purchase totals = $945.15       $1,043.3401   $1,043.33   $1,043.30   $1,043.40