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 $200.56   3.363%   $207.3048   $207.30   $207.30   $207.30  
  Purchase #2 $237.98   10.345%   $262.599   $262.60   $262.60   $262.60  
  Purchase #3 $27.30   8.649%   $29.6612   $29.66   $29.65   $29.70  
  Purchase #4 $109.43   11.480%   $121.9926   $121.99   $122.00   $122.00  
  Purchase #5 $200.70   12.708%   $226.205   $226.21   $226.20   $226.20  
  Purchase #6 $223.84   8.705%   $243.3253   $243.33   $243.35   $243.30  
  Purchase #7 $114.43   3.642%   $118.5975   $118.60   $118.60   $118.60  
  7 purchase totals = $1,114.24       $1,209.6854   $1,209.69   $1,209.70   $1,209.70