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 $213.88   6.587%   $227.9683   $227.97   $227.95   $228.00  
  Purchase #2 $76.32   11.195%   $84.864   $84.86   $84.85   $84.90  
  Purchase #3 $131.91   12.180%   $147.9766   $147.98   $148.00   $148.00  
  Purchase #4 $146.87   4.629%   $153.6686   $153.67   $153.65   $153.70  
  Purchase #5 $80.48   12.432%   $90.4853   $90.49   $90.50   $90.50  
  Purchase #6 $183.55   11.303%   $204.2967   $204.30   $204.30   $204.30  
  Purchase #7 $41.85   13.856%   $47.6487   $47.65   $47.65   $47.60  
  7 purchase totals = $874.86       $956.9082   $956.92   $956.90   $957.00