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 $228.98   3.274%   $236.4768   $236.48   $236.50   $236.50  
  Purchase #2 $17.73   7.740%   $19.1023   $19.10   $19.10   $19.10  
  Purchase #3 $24.78   7.636%   $26.6722   $26.67   $26.65   $26.70  
  Purchase #4 $226.87   8.137%   $245.3304   $245.33   $245.35   $245.30  
  Purchase #5 $91.89   4.477%   $96.0039   $96.00   $96.00   $96.00  
  Purchase #6 $220.62   4.235%   $229.9633   $229.96   $229.95   $230.00  
  Purchase #7 $171.28   4.692%   $179.3165   $179.32   $179.30   $179.30  
  7 purchase totals = $982.15       $1,032.8654   $1,032.86   $1,032.85   $1,032.90