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 $198.32   9.187%   $216.5397   $216.54   $216.55   $216.50  
  Purchase #2 $154.37   9.456%   $168.9672   $168.97   $168.95   $169.00  
  Purchase #3 $209.75   4.253%   $218.6707   $218.67   $218.65   $218.70  
  Purchase #4 $154.49   4.783%   $161.8793   $161.88   $161.90   $161.90  
  Purchase #5 $33.51   3.184%   $34.577   $34.58   $34.60   $34.60  
  Purchase #6 $171.92   7.515%   $184.8398   $184.84   $184.85   $184.80  
  Purchase #7 $32.55   5.383%   $34.3022   $34.30   $34.30   $34.30  
  7 purchase totals = $954.91       $1,019.7759   $1,019.78   $1,019.80   $1,019.80