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 $22.30   11.361%   $24.8335   $24.83   $24.85   $24.80  
  Purchase #2 $226.53   3.284%   $233.9692   $233.97   $233.95   $234.00  
  Purchase #3 $86.55   4.857%   $90.7537   $90.75   $90.75   $90.80  
  Purchase #4 $173.98   3.506%   $180.0797   $180.08   $180.10   $180.10  
  Purchase #5 $229.90   12.528%   $258.7019   $258.70   $258.70   $258.70  
  Purchase #6 $245.47   9.289%   $268.2717   $268.27   $268.25   $268.30  
  Purchase #7 $180.65   8.708%   $196.381   $196.38   $196.40   $196.40  
  7 purchase totals = $1,165.38       $1,252.9907   $1,252.98   $1,253.00   $1,253.10