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 $145.69   10.343%   $160.7587   $160.76   $160.75   $160.80  
  Purchase #2 $25.38   5.388%   $26.7475   $26.75   $26.75   $26.70  
  Purchase #3 $125.55   12.196%   $140.8621   $140.86   $140.85   $140.90  
  Purchase #4 $120.65   10.308%   $133.0866   $133.09   $133.10   $133.10  
  Purchase #5 $226.65   8.239%   $245.3237   $245.32   $245.30   $245.30  
  Purchase #6 $149.29   13.745%   $169.8099   $169.81   $169.80   $169.80  
  Purchase #7 $167.47   11.632%   $186.9501   $186.95   $186.95   $187.00  
  7 purchase totals = $960.68       $1,063.5386   $1,063.54   $1,063.50   $1,063.60