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 $230.96   7.679%   $248.6954   $248.70   $248.70   $248.70  
  Purchase #2 $154.79   12.304%   $173.8354   $173.84   $173.85   $173.80  
  Purchase #3 $41.34   3.724%   $42.8795   $42.88   $42.90   $42.90  
  Purchase #4 $203.57   7.423%   $218.681   $218.68   $218.70   $218.70  
  Purchase #5 $232.55   6.738%   $248.2192   $248.22   $248.20   $248.20  
  Purchase #6 $88.90   5.631%   $93.906   $93.91   $93.90   $93.90  
  Purchase #7 $132.80   7.173%   $142.3257   $142.33   $142.35   $142.30  
  7 purchase totals = $1,084.91       $1,168.5422   $1,168.56   $1,168.60   $1,168.50