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 $241.57   9.368%   $264.2003   $264.20   $264.20   $264.20  
  Purchase #2 $87.87   4.560%   $91.8769   $91.88   $91.90   $91.90  
  Purchase #3 $221.83   8.680%   $241.0848   $241.08   $241.10   $241.10  
  Purchase #4 $86.70   6.535%   $92.3658   $92.37   $92.35   $92.40  
  Purchase #5 $61.32   12.329%   $68.8801   $68.88   $68.90   $68.90  
  Purchase #6 $231.66   6.245%   $246.1272   $246.13   $246.15   $246.10  
  Purchase #7 $179.32   11.848%   $200.5658   $200.57   $200.55   $200.60  
  7 purchase totals = $1,110.27       $1,205.1009   $1,205.11   $1,205.15   $1,205.20