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 $185.41   11.379%   $206.5078   $206.51   $206.50   $206.50  
  Purchase #2 $176.52   9.165%   $192.6981   $192.70   $192.70   $192.70  
  Purchase #3 $160.78   7.516%   $172.8642   $172.86   $172.85   $172.90  
  Purchase #4 $94.43   5.501%   $99.6246   $99.62   $99.60   $99.60  
  Purchase #5 $83.27   4.789%   $87.2578   $87.26   $87.25   $87.30  
  Purchase #6 $187.29   6.652%   $199.7485   $199.75   $199.75   $199.70  
  Purchase #7 $235.33   5.625%   $248.5673   $248.57   $248.55   $248.60  
  7 purchase totals = $1,123.03       $1,207.2683   $1,207.27   $1,207.20   $1,207.30