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 $244.32   13.793%   $278.0191   $278.02   $278.00   $278.00  
  Purchase #2 $131.76   11.247%   $146.579   $146.58   $146.60   $146.60  
  Purchase #3 $73.84   4.547%   $77.1975   $77.20   $77.20   $77.20  
  Purchase #4 $61.49   10.505%   $67.9495   $67.95   $67.95   $67.90  
  Purchase #5 $166.30   11.641%   $185.659   $185.66   $185.65   $185.70  
  Purchase #6 $246.51   7.188%   $264.2291   $264.23   $264.25   $264.20  
  Purchase #7 $172.97   6.362%   $183.9744   $183.97   $183.95   $184.00  
  7 purchase totals = $1,097.19       $1,203.6076   $1,203.61   $1,203.60   $1,203.60