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 $184.54   12.536%   $207.6739   $207.67   $207.65   $207.70  
  Purchase #2 $56.95   3.179%   $58.7604   $58.76   $58.75   $58.80  
  Purchase #3 $153.39   9.611%   $168.1323   $168.13   $168.15   $168.10  
  Purchase #4 $11.69   4.517%   $12.218   $12.22   $12.20   $12.20  
  Purchase #5 $81.72   11.525%   $91.1382   $91.14   $91.15   $91.10  
  Purchase #6 $29.78   11.687%   $33.2604   $33.26   $33.25   $33.30  
  Purchase #7 $189.36   3.864%   $196.6769   $196.68   $196.70   $196.70  
  7 purchase totals = $707.43       $767.8601   $767.86   $767.85   $767.90