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 $57.77   13.742%   $65.7088   $65.71   $65.70   $65.70  
  Purchase #2 $29.39   10.845%   $32.5773   $32.58   $32.60   $32.60  
  Purchase #3 $153.28   4.189%   $159.7009   $159.70   $159.70   $159.70  
  Purchase #4 $222.80   4.165%   $232.0796   $232.08   $232.10   $232.10  
  Purchase #5 $17.59   5.405%   $18.5407   $18.54   $18.55   $18.50  
  Purchase #6 $24.95   4.776%   $26.1416   $26.14   $26.15   $26.10  
  Purchase #7 $201.42   6.238%   $213.9846   $213.98   $214.00   $214.00  
  7 purchase totals = $707.20       $748.7335   $748.73   $748.80   $748.70