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 $91.92   4.542%   $96.095   $96.10   $96.10   $96.10  
  Purchase #2 $24.32   7.508%   $26.1459   $26.15   $26.15   $26.10  
  Purchase #3 $158.33   4.197%   $164.9751   $164.98   $165.00   $165.00  
  Purchase #4 $162.97   12.814%   $183.853   $183.85   $183.85   $183.90  
  Purchase #5 $86.56   8.147%   $93.612   $93.61   $93.60   $93.60  
  Purchase #6 $245.80   9.778%   $269.8343   $269.83   $269.85   $269.80  
  Purchase #7 $230.58   11.740%   $257.6501   $257.65   $257.65   $257.70  
  7 purchase totals = $1,000.48       $1,092.1654   $1,092.17   $1,092.20   $1,092.20