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 $80.61   8.827%   $87.7254   $87.73   $87.75   $87.70  
  Purchase #2 $217.97   13.533%   $247.4679   $247.47   $247.45   $247.50  
  Purchase #3 $9.97   7.157%   $10.6836   $10.68   $10.70   $10.70  
  Purchase #4 $88.51   8.175%   $95.7457   $95.75   $95.75   $95.70  
  Purchase #5 $218.77   12.143%   $245.3352   $245.34   $245.35   $245.30  
  Purchase #6 $211.30   8.677%   $229.6345   $229.63   $229.65   $229.60  
  Purchase #7 $129.86   3.250%   $134.0805   $134.08   $134.10   $134.10  
  7 purchase totals = $956.99       $1,050.6728   $1,050.68   $1,050.75   $1,050.60