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 $104.98   7.759%   $113.1254   $113.13   $113.15   $113.10  
  Purchase #2 $13.94   6.332%   $14.8227   $14.82   $14.80   $14.80  
  Purchase #3 $171.43   5.579%   $180.9941   $180.99   $181.00   $181.00  
  Purchase #4 $161.62   13.613%   $183.6213   $183.62   $183.60   $183.60  
  Purchase #5 $248.61   9.565%   $272.3895   $272.39   $272.40   $272.40  
  Purchase #6 $207.92   8.821%   $226.2606   $226.26   $226.25   $226.30  
  Purchase #7 $179.83   11.443%   $200.4079   $200.41   $200.40   $200.40  
  7 purchase totals = $1,088.33       $1,191.6215   $1,191.62   $1,191.60   $1,191.60