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 $209.48   11.257%   $233.0612   $233.06   $233.05   $233.10  
  Purchase #2 $174.76   3.702%   $181.2296   $181.23   $181.25   $181.20  
  Purchase #3 $147.99   13.750%   $168.3386   $168.34   $168.35   $168.30  
  Purchase #4 $117.62   5.799%   $124.4408   $124.44   $124.45   $124.40  
  Purchase #5 $184.98   12.235%   $207.6123   $207.61   $207.60   $207.60  
  Purchase #6 $192.34   12.223%   $215.8497   $215.85   $215.85   $215.80  
  Purchase #7 $63.71   5.654%   $67.3122   $67.31   $67.30   $67.30  
  7 purchase totals = $1,090.88       $1,197.8444   $1,197.84   $1,197.85   $1,197.70