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 $99.91   13.549%   $113.4468   $113.45   $113.45   $113.40  
  Purchase #2 $232.25   9.602%   $254.5506   $254.55   $254.55   $254.60  
  Purchase #3 $238.87   13.311%   $270.666   $270.67   $270.65   $270.70  
  Purchase #4 $145.69   13.865%   $165.8899   $165.89   $165.90   $165.90  
  Purchase #5 $103.45   4.148%   $107.7411   $107.74   $107.75   $107.70  
  Purchase #6 $139.39   11.437%   $155.332   $155.33   $155.35   $155.30  
  Purchase #7 $7.50   6.618%   $7.9964   $8.00   $8.00   $8.00  
  7 purchase totals = $967.06       $1,075.6228   $1,075.63   $1,075.65   $1,075.60