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 $243.29   13.557%   $276.2728   $276.27   $276.25   $276.30  
  Purchase #2 $201.84   8.371%   $218.736   $218.74   $218.75   $218.70  
  Purchase #3 $196.68   3.495%   $203.554   $203.55   $203.55   $203.60  
  Purchase #4 $54.71   13.177%   $61.9191   $61.92   $61.90   $61.90  
  Purchase #5 $97.55   4.581%   $102.0188   $102.02   $102.00   $102.00  
  Purchase #6 $159.80   12.407%   $179.6264   $179.63   $179.65   $179.60  
  Purchase #7 $9.41   10.219%   $10.3716   $10.37   $10.35   $10.40  
  7 purchase totals = $963.28       $1,052.4987   $1,052.50   $1,052.45   $1,052.50