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 $219.77   11.728%   $245.5446   $245.54   $245.55   $245.50  
  Purchase #2 $58.73   4.107%   $61.142   $61.14   $61.15   $61.10  
  Purchase #3 $8.96   8.570%   $9.7279   $9.73   $9.75   $9.70  
  Purchase #4 $250.67   9.781%   $275.188   $275.19   $275.20   $275.20  
  Purchase #5 $65.98   7.145%   $70.6943   $70.69   $70.70   $70.70  
  Purchase #6 $250.32   4.864%   $262.4956   $262.50   $262.50   $262.50  
  Purchase #7 $82.73   13.140%   $93.6007   $93.60   $93.60   $93.60  
  7 purchase totals = $937.16       $1,018.3931   $1,018.39   $1,018.45   $1,018.30