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 $205.55   8.869%   $223.7802   $223.78   $223.80   $223.80  
  Purchase #2 $50.60   12.406%   $56.8774   $56.88   $56.90   $56.90  
  Purchase #3 $175.88   10.790%   $194.8575   $194.86   $194.85   $194.90  
  Purchase #4 $205.51   10.267%   $226.6097   $226.61   $226.60   $226.60  
  Purchase #5 $91.29   6.602%   $97.317   $97.32   $97.30   $97.30  
  Purchase #6 $158.42   5.233%   $166.7101   $166.71   $166.70   $166.70  
  Purchase #7 $57.40   5.690%   $60.6661   $60.67   $60.65   $60.70  
  7 purchase totals = $944.65       $1,026.8180   $1,026.83   $1,026.80   $1,026.90