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 $195.74   13.430%   $222.0279   $222.03   $222.05   $222.00  
  Purchase #2 $167.79   5.461%   $176.953   $176.95   $176.95   $177.00  
  Purchase #3 $241.46   11.825%   $270.0126   $270.01   $270.00   $270.00  
  Purchase #4 $81.50   5.266%   $85.7918   $85.79   $85.80   $85.80  
  Purchase #5 $162.31   6.563%   $172.9624   $172.96   $172.95   $173.00  
  Purchase #6 $94.25   10.205%   $103.8682   $103.87   $103.85   $103.90  
  Purchase #7 $232.85   5.788%   $246.3274   $246.33   $246.35   $246.30  
  7 purchase totals = $1,175.90       $1,277.9433   $1,277.94   $1,277.95   $1,278.00