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 $84.34   12.786%   $95.1237   $95.12   $95.10   $95.10  
  Purchase #2 $87.52   3.711%   $90.7679   $90.77   $90.75   $90.80  
  Purchase #3 $19.59   6.534%   $20.87   $20.87   $20.85   $20.90  
  Purchase #4 $209.82   7.333%   $225.2061   $225.21   $225.20   $225.20  
  Purchase #5 $7.25   5.803%   $7.6707   $7.67   $7.65   $7.70  
  Purchase #6 $113.92   4.690%   $119.2628   $119.26   $119.25   $119.30  
  Purchase #7 $34.85   9.151%   $38.0391   $38.04   $38.05   $38.00  
  7 purchase totals = $557.29       $596.9403   $596.94   $596.85   $597.00