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 $192.98   6.683%   $205.8769   $205.88   $205.90   $205.90  
  Purchase #2 $230.66   9.483%   $252.5335   $252.53   $252.55   $252.50  
  Purchase #3 $91.84   6.374%   $97.6939   $97.69   $97.70   $97.70  
  Purchase #4 $45.43   4.450%   $47.4516   $47.45   $47.45   $47.50  
  Purchase #5 $216.28   4.142%   $225.2383   $225.24   $225.25   $225.20  
  Purchase #6 $196.59   10.160%   $216.5635   $216.56   $216.55   $216.60  
  Purchase #7 $17.44   5.629%   $18.4217   $18.42   $18.40   $18.40  
  7 purchase totals = $991.22       $1,063.7794   $1,063.77   $1,063.80   $1,063.80