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 $168.53   5.146%   $177.2026   $177.20   $177.20   $177.20  
  Purchase #2 $51.54   3.787%   $53.4918   $53.49   $53.50   $53.50  
  Purchase #3 $63.85   8.233%   $69.1068   $69.11   $69.10   $69.10  
  Purchase #4 $14.57   10.108%   $16.0427   $16.04   $16.05   $16.00  
  Purchase #5 $53.33   6.779%   $56.9452   $56.95   $56.95   $56.90  
  Purchase #6 $170.53   12.304%   $191.512   $191.51   $191.50   $191.50  
  Purchase #7 $175.60   12.180%   $196.9881   $196.99   $197.00   $197.00  
  7 purchase totals = $697.95       $761.2892   $761.29   $761.30   $761.20