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 $88.87   5.126%   $93.4255   $93.43   $93.45   $93.40  
  Purchase #2 $168.70   5.483%   $177.9498   $177.95   $177.95   $177.90  
  Purchase #3 $156.67   6.612%   $167.029   $167.03   $167.05   $167.00  
  Purchase #4 $212.46   9.554%   $232.7584   $232.76   $232.75   $232.80  
  Purchase #5 $195.82   11.743%   $218.8151   $218.82   $218.80   $218.80  
  Purchase #6 $152.28   5.757%   $161.0468   $161.05   $161.05   $161.00  
  Purchase #7 $51.98   8.199%   $56.2418   $56.24   $56.25   $56.20  
  7 purchase totals = $1,026.78       $1,107.2664   $1,107.28   $1,107.30   $1,107.10