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 $188.93   7.290%   $202.703   $202.70   $202.70   $202.70  
  Purchase #2 $232.52   7.444%   $249.8288   $249.83   $249.85   $249.80  
  Purchase #3 $118.57   9.702%   $130.0737   $130.07   $130.05   $130.10  
  Purchase #4 $137.30   7.529%   $147.6373   $147.64   $147.65   $147.60  
  Purchase #5 $79.66   8.737%   $86.6199   $86.62   $86.60   $86.60  
  Purchase #6 $171.50   12.196%   $192.4161   $192.42   $192.40   $192.40  
  Purchase #7 $168.60   3.175%   $173.9531   $173.95   $173.95   $174.00  
  7 purchase totals = $1,097.08       $1,183.2319   $1,183.23   $1,183.20   $1,183.20