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 $202.93   5.301%   $213.6873   $213.69   $213.70   $213.70  
  Purchase #2 $97.44   9.683%   $106.8751   $106.88   $106.90   $106.90  
  Purchase #3 $216.25   11.566%   $241.2615   $241.26   $241.25   $241.30  
  Purchase #4 $155.32   4.636%   $162.5206   $162.52   $162.50   $162.50  
  Purchase #5 $178.90   11.666%   $199.7705   $199.77   $199.75   $199.80  
  Purchase #6 $191.35   3.760%   $198.5448   $198.54   $198.55   $198.50  
  Purchase #7 $222.50   8.320%   $241.012   $241.01   $241.00   $241.00  
  7 purchase totals = $1,264.69       $1,363.6718   $1,363.67   $1,363.65   $1,363.70