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 $168.77   10.658%   $186.7575   $186.76   $186.75   $186.80  
  Purchase #2 $192.63   6.687%   $205.5112   $205.51   $205.50   $205.50  
  Purchase #3 $27.35   7.655%   $29.4436   $29.44   $29.45   $29.40  
  Purchase #4 $64.25   6.444%   $68.3903   $68.39   $68.40   $68.40  
  Purchase #5 $8.82   4.188%   $9.1894   $9.19   $9.20   $9.20  
  Purchase #6 $174.86   10.507%   $193.2325   $193.23   $193.25   $193.20  
  Purchase #7 $70.61   3.516%   $73.0926   $73.09   $73.10   $73.10  
  7 purchase totals = $707.29       $765.6171   $765.61   $765.65   $765.60