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 $21.83   13.738%   $24.829   $24.83   $24.85   $24.80  
  Purchase #2 $231.57   11.256%   $257.6355   $257.64   $257.65   $257.60  
  Purchase #3 $186.30   13.616%   $211.6666   $211.67   $211.65   $211.70  
  Purchase #4 $215.47   9.730%   $236.4352   $236.44   $236.45   $236.40  
  Purchase #5 $10.32   4.264%   $10.76   $10.76   $10.75   $10.80  
  Purchase #6 $240.61   13.282%   $272.5678   $272.57   $272.55   $272.60  
  Purchase #7 $71.82   4.479%   $75.0368   $75.04   $75.05   $75.00  
  7 purchase totals = $977.92       $1,088.9309   $1,088.95   $1,088.95   $1,088.90