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 $46.53   5.287%   $48.99   $48.99   $49.00   $49.00  
  Purchase #2 $56.87   12.445%   $63.9475   $63.95   $63.95   $63.90  
  Purchase #3 $20.25   6.322%   $21.5302   $21.53   $21.55   $21.50  
  Purchase #4 $203.85   8.508%   $221.1936   $221.19   $221.20   $221.20  
  Purchase #5 $188.25   12.118%   $211.0621   $211.06   $211.05   $211.10  
  Purchase #6 $239.29   10.527%   $264.4801   $264.48   $264.50   $264.50  
  Purchase #7 $26.66   12.197%   $29.9117   $29.91   $29.90   $29.90  
  7 purchase totals = $781.70       $861.1152   $861.11   $861.15   $861.10