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 $182.66   8.121%   $197.4938   $197.49   $197.50   $197.50  
  Purchase #2 $167.35   6.307%   $177.9048   $177.90   $177.90   $177.90  
  Purchase #3 $22.55   5.450%   $23.779   $23.78   $23.80   $23.80  
  Purchase #4 $81.32   12.177%   $91.2223   $91.22   $91.20   $91.20  
  Purchase #5 $235.48   7.572%   $253.3105   $253.31   $253.30   $253.30  
  Purchase #6 $179.32   5.369%   $188.9477   $188.95   $188.95   $188.90  
  Purchase #7 $196.77   4.279%   $205.1898   $205.19   $205.20   $205.20  
  7 purchase totals = $1,065.45       $1,137.8479   $1,137.84   $1,137.85   $1,137.80