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 $87.78   8.829%   $95.5301   $95.53   $95.55   $95.50  
  Purchase #2 $115.66   12.594%   $130.2262   $130.23   $130.25   $130.20  
  Purchase #3 $105.69   6.698%   $112.7691   $112.77   $112.75   $112.80  
  Purchase #4 $157.58   8.796%   $171.4407   $171.44   $171.45   $171.40  
  Purchase #5 $165.80   4.122%   $172.6343   $172.63   $172.65   $172.60  
  Purchase #6 $183.79   4.852%   $192.7075   $192.71   $192.70   $192.70  
  Purchase #7 $181.82   6.278%   $193.2347   $193.23   $193.25   $193.20  
  7 purchase totals = $998.12       $1,068.5426   $1,068.54   $1,068.60   $1,068.40