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 $30.58   6.580%   $32.5922   $32.59   $32.60   $32.60  
  Purchase #2 $99.77   9.118%   $108.867   $108.87   $108.85   $108.90  
  Purchase #3 $113.93   11.186%   $126.6742   $126.67   $126.65   $126.70  
  Purchase #4 $236.28   6.200%   $250.9294   $250.93   $250.95   $250.90  
  Purchase #5 $85.81   11.618%   $95.7794   $95.78   $95.80   $95.80  
  Purchase #6 $215.27   8.704%   $234.0071   $234.01   $234.00   $234.00  
  Purchase #7 $236.33   6.507%   $251.708   $251.71   $251.70   $251.70  
  7 purchase totals = $1,017.97       $1,100.5573   $1,100.56   $1,100.55   $1,100.60