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 $100.70   4.529%   $105.2607   $105.26   $105.25   $105.30  
  Purchase #2 $83.48   6.346%   $88.7776   $88.78   $88.80   $88.80  
  Purchase #3 $5.30   8.686%   $5.7604   $5.76   $5.75   $5.80  
  Purchase #4 $160.66   7.338%   $172.4492   $172.45   $172.45   $172.40  
  Purchase #5 $178.31   12.127%   $199.9337   $199.93   $199.95   $199.90  
  Purchase #6 $36.79   13.206%   $41.6485   $41.65   $41.65   $41.60  
  Purchase #7 $177.40   10.484%   $195.9986   $196.00   $196.00   $196.00  
  7 purchase totals = $742.64       $809.8287   $809.83   $809.85   $809.80