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 $100.56   5.640%   $106.2316   $106.23   $106.25   $106.20  
  Purchase #2 $19.60   9.189%   $21.401   $21.40   $21.40   $21.40  
  Purchase #3 $207.31   11.828%   $231.8306   $231.83   $231.85   $231.80  
  Purchase #4 $211.48   7.698%   $227.7597   $227.76   $227.75   $227.80  
  Purchase #5 $246.31   9.724%   $270.2612   $270.26   $270.25   $270.30  
  Purchase #6 $188.92   7.150%   $202.4278   $202.43   $202.45   $202.40  
  Purchase #7 $75.87   8.570%   $82.3721   $82.37   $82.35   $82.40  
  7 purchase totals = $1,050.05       $1,142.2840   $1,142.28   $1,142.30   $1,142.30