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 $211.56   5.410%   $223.0054   $223.01   $223.00   $223.00  
  Purchase #2 $28.96   10.247%   $31.9275   $31.93   $31.95   $31.90  
  Purchase #3 $220.99   7.735%   $238.0836   $238.08   $238.10   $238.10  
  Purchase #4 $168.88   8.304%   $182.9038   $182.90   $182.90   $182.90  
  Purchase #5 $64.41   13.361%   $73.0158   $73.02   $73.00   $73.00  
  Purchase #6 $232.31   7.652%   $250.0864   $250.09   $250.10   $250.10  
  Purchase #7 $247.95   3.234%   $255.9687   $255.97   $255.95   $256.00  
  7 purchase totals = $1,175.06       $1,254.9912   $1,255.00   $1,255.00   $1,255.00