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 $241.77   6.792%   $258.191   $258.19   $258.20   $258.20  
  Purchase #2 $245.75   3.822%   $255.1426   $255.14   $255.15   $255.10  
  Purchase #3 $31.94   4.829%   $33.4824   $33.48   $33.50   $33.50  
  Purchase #4 $235.37   13.394%   $266.8955   $266.90   $266.90   $266.90  
  Purchase #5 $59.28   11.620%   $66.1683   $66.17   $66.15   $66.20  
  Purchase #6 $72.34   10.711%   $80.0883   $80.09   $80.10   $80.10  
  Purchase #7 $84.55   12.384%   $95.0207   $95.02   $95.00   $95.00  
  7 purchase totals = $971.00       $1,054.9888   $1,054.99   $1,055.00   $1,055.00