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 $5.67   7.122%   $6.0738   $6.07   $6.05   $6.10  
  Purchase #2 $231.41   8.520%   $251.1261   $251.13   $251.15   $251.10  
  Purchase #3 $206.84   5.118%   $217.4261   $217.43   $217.45   $217.40  
  Purchase #4 $183.58   11.866%   $205.3636   $205.36   $205.35   $205.40  
  Purchase #5 $243.89   4.702%   $255.3577   $255.36   $255.35   $255.40  
  Purchase #6 $43.99   8.784%   $47.8541   $47.85   $47.85   $47.90  
  Purchase #7 $66.65   4.345%   $69.5459   $69.55   $69.55   $69.50  
  7 purchase totals = $982.03       $1,052.7473   $1,052.75   $1,052.75   $1,052.80