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 $181.93   8.708%   $197.7725   $197.77   $197.75   $197.80  
  Purchase #2 $172.30   5.272%   $181.3837   $181.38   $181.40   $181.40  
  Purchase #3 $118.89   7.607%   $127.934   $127.93   $127.95   $127.90  
  Purchase #4 $72.41   4.117%   $75.3911   $75.39   $75.40   $75.40  
  Purchase #5 $140.83   12.486%   $158.414   $158.41   $158.40   $158.40  
  Purchase #6 $53.65   11.311%   $59.7184   $59.72   $59.70   $59.70  
  Purchase #7 $232.62   11.841%   $260.1645   $260.16   $260.15   $260.20  
  7 purchase totals = $972.63       $1,060.7782   $1,060.76   $1,060.75   $1,060.80