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 $240.57   13.353%   $272.6933   $272.69   $272.70   $272.70  
  Purchase #2 $197.97   7.394%   $212.6079   $212.61   $212.60   $212.60  
  Purchase #3 $244.68   13.693%   $278.184   $278.18   $278.20   $278.20  
  Purchase #4 $108.84   3.280%   $112.41   $112.41   $112.40   $112.40  
  Purchase #5 $185.70   8.811%   $202.062   $202.06   $202.05   $202.10  
  Purchase #6 $114.84   6.164%   $121.9187   $121.92   $121.90   $121.90  
  Purchase #7 $249.37   13.470%   $282.9601   $282.96   $282.95   $283.00  
  7 purchase totals = $1,341.97       $1,482.8360   $1,482.83   $1,482.80   $1,482.90