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 $183.32   9.746%   $201.1864   $201.19   $201.20   $201.20  
  Purchase #2 $226.61   10.613%   $250.6601   $250.66   $250.65   $250.70  
  Purchase #3 $37.87   10.120%   $41.7024   $41.70   $41.70   $41.70  
  Purchase #4 $80.48   10.363%   $88.8201   $88.82   $88.80   $88.80  
  Purchase #5 $16.66   4.562%   $17.42   $17.42   $17.40   $17.40  
  Purchase #6 $228.27   10.260%   $251.6905   $251.69   $251.70   $251.70  
  Purchase #7 $51.42   11.270%   $57.215   $57.22   $57.20   $57.20  
  7 purchase totals = $824.63       $908.6945   $908.70   $908.65   $908.70