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 $176.51   5.262%   $185.798   $185.80   $185.80   $185.80  
  Purchase #2 $41.55   7.447%   $44.6442   $44.64   $44.65   $44.60  
  Purchase #3 $58.79   4.668%   $61.5343   $61.53   $61.55   $61.50  
  Purchase #4 $28.59   7.562%   $30.752   $30.75   $30.75   $30.80  
  Purchase #5 $52.62   5.501%   $55.5146   $55.51   $55.50   $55.50  
  Purchase #6 $177.26   5.455%   $186.9295   $186.93   $186.95   $186.90  
  Purchase #7 $189.93   8.123%   $205.358   $205.36   $205.35   $205.40  
  7 purchase totals = $725.25       $770.5306   $770.52   $770.55   $770.50