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 $53.91   10.296%   $59.4606   $59.46   $59.45   $59.50  
  Purchase #2 $68.79   8.549%   $74.6709   $74.67   $74.65   $74.70  
  Purchase #3 $235.77   9.664%   $258.5548   $258.55   $258.55   $258.60  
  Purchase #4 $92.38   5.780%   $97.7196   $97.72   $97.70   $97.70  
  Purchase #5 $219.42   12.688%   $247.26   $247.26   $247.25   $247.30  
  Purchase #6 $165.53   9.617%   $181.449   $181.45   $181.45   $181.40  
  Purchase #7 $250.27   13.198%   $283.3006   $283.30   $283.30   $283.30  
  7 purchase totals = $1,086.07       $1,202.4155   $1,202.41   $1,202.35   $1,202.50