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 $86.97   13.651%   $98.8423   $98.84   $98.85   $98.80  
  Purchase #2 $63.86   4.222%   $66.5562   $66.56   $66.55   $66.60  
  Purchase #3 $178.55   12.779%   $201.3669   $201.37   $201.35   $201.40  
  Purchase #4 $235.48   10.420%   $260.017   $260.02   $260.00   $260.00  
  Purchase #5 $247.63   6.275%   $263.1688   $263.17   $263.15   $263.20  
  Purchase #6 $27.41   9.298%   $29.9586   $29.96   $29.95   $30.00  
  Purchase #7 $210.46   9.419%   $230.2832   $230.28   $230.30   $230.30  
  7 purchase totals = $1,050.36       $1,150.1930   $1,150.20   $1,150.15   $1,150.30