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 $64.81   4.431%   $67.6817   $67.68   $67.70   $67.70  
  Purchase #2 $203.36   7.520%   $218.6527   $218.65   $218.65   $218.70  
  Purchase #3 $164.61   12.327%   $184.9015   $184.90   $184.90   $184.90  
  Purchase #4 $11.58   11.807%   $12.9473   $12.95   $12.95   $12.90  
  Purchase #5 $241.85   11.592%   $269.8853   $269.89   $269.90   $269.90  
  Purchase #6 $181.62   10.190%   $200.1271   $200.13   $200.15   $200.10  
  Purchase #7 $232.53   8.211%   $251.623   $251.62   $251.60   $251.60  
  7 purchase totals = $1,100.36       $1,205.8186   $1,205.82   $1,205.85   $1,205.80