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 $232.44   3.522%   $240.6265   $240.63   $240.65   $240.60  
  Purchase #2 $86.79   5.696%   $91.7336   $91.73   $91.75   $91.70  
  Purchase #3 $31.98   6.826%   $34.163   $34.16   $34.15   $34.20  
  Purchase #4 $41.48   11.195%   $46.1237   $46.12   $46.10   $46.10  
  Purchase #5 $200.74   12.705%   $226.244   $226.24   $226.25   $226.20  
  Purchase #6 $66.61   6.315%   $70.8164   $70.82   $70.80   $70.80  
  Purchase #7 $215.35   11.840%   $240.8474   $240.85   $240.85   $240.80  
  7 purchase totals = $875.39       $950.5546   $950.55   $950.55   $950.40