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 $229.39   5.176%   $241.2632   $241.26   $241.25   $241.30  
  Purchase #2 $221.45   7.123%   $237.2239   $237.22   $237.20   $237.20  
  Purchase #3 $53.44   12.174%   $59.9458   $59.95   $59.95   $59.90  
  Purchase #4 $193.28   6.479%   $205.8026   $205.80   $205.80   $205.80  
  Purchase #5 $121.95   9.519%   $133.5584   $133.56   $133.55   $133.60  
  Purchase #6 $60.65   5.371%   $63.9075   $63.91   $63.90   $63.90  
  Purchase #7 $210.49   9.535%   $230.5602   $230.56   $230.55   $230.60  
  7 purchase totals = $1,090.65       $1,172.2616   $1,172.26   $1,172.20   $1,172.30