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 $173.75   7.838%   $187.3685   $187.37   $187.35   $187.40  
  Purchase #2 $239.30   5.769%   $253.1052   $253.11   $253.10   $253.10  
  Purchase #3 $198.36   12.589%   $223.3315   $223.33   $223.35   $223.30  
  Purchase #4 $150.43   5.169%   $158.2057   $158.21   $158.20   $158.20  
  Purchase #5 $200.44   9.386%   $219.2533   $219.25   $219.25   $219.30  
  Purchase #6 $151.27   10.449%   $167.0762   $167.08   $167.10   $167.10  
  Purchase #7 $183.47   9.397%   $200.7107   $200.71   $200.70   $200.70  
  7 purchase totals = $1,297.02       $1,409.0511   $1,409.06   $1,409.05   $1,409.10