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 $210.94   10.139%   $232.3272   $232.33   $232.35   $232.30  
  Purchase #2 $86.43   6.591%   $92.1266   $92.13   $92.15   $92.10  
  Purchase #3 $145.49   8.419%   $157.7388   $157.74   $157.75   $157.70  
  Purchase #4 $219.31   6.265%   $233.0498   $233.05   $233.05   $233.00  
  Purchase #5 $134.55   5.404%   $141.8211   $141.82   $141.80   $141.80  
  Purchase #6 $77.25   10.362%   $85.2546   $85.25   $85.25   $85.30  
  Purchase #7 $93.90   12.834%   $105.9511   $105.95   $105.95   $106.00  
  7 purchase totals = $967.87       $1,048.2692   $1,048.27   $1,048.30   $1,048.20