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 $194.70   5.765%   $205.9245   $205.92   $205.90   $205.90  
  Purchase #2 $95.99   12.161%   $107.6633   $107.66   $107.65   $107.70  
  Purchase #3 $54.43   11.538%   $60.7101   $60.71   $60.70   $60.70  
  Purchase #4 $236.77   3.210%   $244.3703   $244.37   $244.35   $244.40  
  Purchase #5 $183.46   8.505%   $199.0633   $199.06   $199.05   $199.10  
  Purchase #6 $150.84   13.451%   $171.1295   $171.13   $171.15   $171.10  
  Purchase #7 $78.56   11.761%   $87.7994   $87.80   $87.80   $87.80  
  7 purchase totals = $994.75       $1,076.6604   $1,076.65   $1,076.60   $1,076.70