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 $207.99   10.156%   $229.1135   $229.11   $229.10   $229.10  
  Purchase #2 $237.37   3.623%   $245.9699   $245.97   $245.95   $246.00  
  Purchase #3 $82.65   13.456%   $93.7714   $93.77   $93.75   $93.80  
  Purchase #4 $107.94   5.855%   $114.2599   $114.26   $114.25   $114.30  
  Purchase #5 $180.63   11.759%   $201.8703   $201.87   $201.85   $201.90  
  Purchase #6 $64.51   12.442%   $72.5363   $72.54   $72.55   $72.50  
  Purchase #7 $94.58   8.747%   $102.8529   $102.85   $102.85   $102.90  
  7 purchase totals = $975.67       $1,060.3742   $1,060.37   $1,060.30   $1,060.50