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 $61.72   13.241%   $69.8923   $69.89   $69.90   $69.90  
  Purchase #2 $183.25   11.841%   $204.9486   $204.95   $204.95   $204.90  
  Purchase #3 $212.74   3.295%   $219.7498   $219.75   $219.75   $219.70  
  Purchase #4 $195.26   5.260%   $205.5307   $205.53   $205.55   $205.50  
  Purchase #5 $183.79   11.204%   $204.3818   $204.38   $204.40   $204.40  
  Purchase #6 $249.78   11.326%   $278.0701   $278.07   $278.05   $278.10  
  Purchase #7 $46.93   7.754%   $50.569   $50.57   $50.55   $50.60  
  7 purchase totals = $1,133.47       $1,233.1423   $1,233.14   $1,233.15   $1,233.10