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 $83.83   8.497%   $90.953   $90.95   $90.95   $91.00  
  Purchase #2 $232.99   6.300%   $247.6684   $247.67   $247.65   $247.70  
  Purchase #3 $26.86   6.799%   $28.6862   $28.69   $28.70   $28.70  
  Purchase #4 $22.80   13.241%   $25.8189   $25.82   $25.80   $25.80  
  Purchase #5 $54.36   13.291%   $61.585   $61.59   $61.60   $61.60  
  Purchase #6 $238.87   6.533%   $254.4754   $254.48   $254.50   $254.50  
  Purchase #7 $244.93   10.329%   $270.2288   $270.23   $270.25   $270.20  
  7 purchase totals = $904.64       $979.4157   $979.43   $979.45   $979.50