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 $208.89   4.691%   $218.689   $218.69   $218.70   $218.70  
  Purchase #2 $129.35   11.285%   $143.9471   $143.95   $143.95   $143.90  
  Purchase #3 $29.75   4.638%   $31.1298   $31.13   $31.15   $31.10  
  Purchase #4 $159.79   12.156%   $179.2141   $179.21   $179.20   $179.20  
  Purchase #5 $54.37   11.290%   $60.5084   $60.51   $60.50   $60.50  
  Purchase #6 $167.73   9.197%   $183.1561   $183.16   $183.15   $183.20  
  Purchase #7 $196.79   12.790%   $221.9594   $221.96   $221.95   $222.00  
  7 purchase totals = $946.67       $1,038.6039   $1,038.61   $1,038.60   $1,038.60