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 $68.93   8.453%   $74.7567   $74.76   $74.75   $74.80  
  Purchase #2 $219.80   4.145%   $228.9107   $228.91   $228.90   $228.90  
  Purchase #3 $224.91   10.553%   $248.6448   $248.64   $248.65   $248.60  
  Purchase #4 $119.69   9.866%   $131.4986   $131.50   $131.50   $131.50  
  Purchase #5 $60.44   4.143%   $62.944   $62.94   $62.95   $62.90  
  Purchase #6 $244.96   11.526%   $273.1941   $273.19   $273.20   $273.20  
  Purchase #7 $40.44   12.751%   $45.5965   $45.60   $45.60   $45.60  
  7 purchase totals = $979.17       $1,065.5454   $1,065.54   $1,065.55   $1,065.50