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 $82.83   6.284%   $88.035   $88.04   $88.05   $88.00  
  Purchase #2 $240.47   9.658%   $263.6946   $263.69   $263.70   $263.70  
  Purchase #3 $244.27   5.328%   $257.2847   $257.28   $257.30   $257.30  
  Purchase #4 $228.86   6.550%   $243.8503   $243.85   $243.85   $243.90  
  Purchase #5 $116.35   3.727%   $120.6864   $120.69   $120.70   $120.70  
  Purchase #6 $84.61   11.325%   $94.1921   $94.19   $94.20   $94.20  
  Purchase #7 $5.85   5.247%   $6.1569   $6.16   $6.15   $6.20  
  7 purchase totals = $1,003.24       $1,073.9000   $1,073.90   $1,073.95   $1,074.00