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 $52.77   4.846%   $55.3272   $55.33   $55.35   $55.30  
  Purchase #2 $96.55   8.301%   $104.5646   $104.56   $104.55   $104.60  
  Purchase #3 $34.37   8.562%   $37.3128   $37.31   $37.30   $37.30  
  Purchase #4 $156.60   8.364%   $169.698   $169.70   $169.70   $169.70  
  Purchase #5 $181.93   8.648%   $197.6633   $197.66   $197.65   $197.70  
  Purchase #6 $222.68   12.270%   $250.0028   $250.00   $250.00   $250.00  
  Purchase #7 $120.51   7.612%   $129.6832   $129.68   $129.70   $129.70  
  7 purchase totals = $865.41       $944.2519   $944.24   $944.25   $944.30