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 $54.55   13.818%   $62.0877   $62.09   $62.10   $62.10  
  Purchase #2 $245.42   13.622%   $278.8511   $278.85   $278.85   $278.90  
  Purchase #3 $211.88   6.661%   $225.9933   $225.99   $226.00   $226.00  
  Purchase #4 $95.98   10.844%   $106.3881   $106.39   $106.40   $106.40  
  Purchase #5 $211.90   4.144%   $220.6811   $220.68   $220.70   $220.70  
  Purchase #6 $22.97   3.121%   $23.6869   $23.69   $23.70   $23.70  
  Purchase #7 $98.69   4.560%   $103.1903   $103.19   $103.20   $103.20  
  7 purchase totals = $941.39       $1,020.8785   $1,020.88   $1,020.95   $1,021.00