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 $67.51   8.630%   $73.3361   $73.34   $73.35   $73.30  
  Purchase #2 $177.65   11.213%   $197.5699   $197.57   $197.55   $197.60  
  Purchase #3 $163.67   5.327%   $172.3887   $172.39   $172.40   $172.40  
  Purchase #4 $44.87   7.753%   $48.3488   $48.35   $48.35   $48.30  
  Purchase #5 $202.59   3.675%   $210.0352   $210.04   $210.05   $210.00  
  Purchase #6 $7.87   4.384%   $8.215   $8.22   $8.20   $8.20  
  Purchase #7 $49.25   12.570%   $55.4407   $55.44   $55.45   $55.40  
  7 purchase totals = $713.41       $765.3344   $765.35   $765.35   $765.20