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 $199.78   13.195%   $226.141   $226.14   $226.15   $226.10  
  Purchase #2 $61.73   11.476%   $68.8141   $68.81   $68.80   $68.80  
  Purchase #3 $233.37   5.638%   $246.5274   $246.53   $246.55   $246.50  
  Purchase #4 $62.32   4.282%   $64.9885   $64.99   $65.00   $65.00  
  Purchase #5 $98.81   7.521%   $106.2415   $106.24   $106.25   $106.20  
  Purchase #6 $108.64   4.744%   $113.7939   $113.79   $113.80   $113.80  
  Purchase #7 $167.67   9.634%   $183.8233   $183.82   $183.80   $183.80  
  7 purchase totals = $932.32       $1,010.3297   $1,010.32   $1,010.35   $1,010.20