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 $203.87   7.452%   $219.0624   $219.06   $219.05   $219.10  
  Purchase #2 $145.38   10.638%   $160.8455   $160.85   $160.85   $160.80  
  Purchase #3 $75.71   11.753%   $84.6082   $84.61   $84.60   $84.60  
  Purchase #4 $183.26   7.552%   $197.0998   $197.10   $197.10   $197.10  
  Purchase #5 $250.88   9.496%   $274.7036   $274.70   $274.70   $274.70  
  Purchase #6 $241.75   13.565%   $274.5434   $274.54   $274.55   $274.50  
  Purchase #7 $248.58   13.367%   $281.8077   $281.81   $281.80   $281.80  
  7 purchase totals = $1,349.43       $1,492.6706   $1,492.67   $1,492.65   $1,492.60