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 $239.61   10.588%   $264.9799   $264.98   $265.00   $265.00  
  Purchase #2 $34.37   10.855%   $38.1009   $38.10   $38.10   $38.10  
  Purchase #3 $120.87   10.653%   $133.7463   $133.75   $133.75   $133.70  
  Purchase #4 $8.72   9.229%   $9.5248   $9.52   $9.50   $9.50  
  Purchase #5 $107.72   13.802%   $122.5875   $122.59   $122.60   $122.60  
  Purchase #6 $86.98   11.124%   $96.6557   $96.66   $96.65   $96.70  
  Purchase #7 $90.28   12.296%   $101.3808   $101.38   $101.40   $101.40  
  7 purchase totals = $688.55       $766.9759   $766.98   $767.00   $767.00