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 $30.63   9.699%   $33.6008   $33.60   $33.60   $33.60  
  Purchase #2 $143.90   6.219%   $152.8491   $152.85   $152.85   $152.80  
  Purchase #3 $54.29   6.332%   $57.7276   $57.73   $57.75   $57.70  
  Purchase #4 $61.82   6.606%   $65.9038   $65.90   $65.90   $65.90  
  Purchase #5 $87.68   7.155%   $93.9535   $93.95   $93.95   $94.00  
  Purchase #6 $111.92   7.856%   $120.7124   $120.71   $120.70   $120.70  
  Purchase #7 $225.93   4.744%   $236.6481   $236.65   $236.65   $236.60  
  7 purchase totals = $716.17       $761.3953   $761.39   $761.40   $761.30