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 $118.84   12.409%   $133.5869   $133.59   $133.60   $133.60  
  Purchase #2 $25.29   5.579%   $26.7009   $26.70   $26.70   $26.70  
  Purchase #3 $152.96   11.693%   $170.8456   $170.85   $170.85   $170.80  
  Purchase #4 $233.36   3.600%   $241.761   $241.76   $241.75   $241.80  
  Purchase #5 $106.90   5.127%   $112.3808   $112.38   $112.40   $112.40  
  Purchase #6 $49.41   6.791%   $52.7654   $52.77   $52.75   $52.80  
  Purchase #7 $13.64   6.795%   $14.5668   $14.57   $14.55   $14.60  
  7 purchase totals = $700.40       $752.6074   $752.62   $752.60   $752.70