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 $160.64   12.361%   $180.4967   $180.50   $180.50   $180.50  
  Purchase #2 $196.84   13.653%   $223.7146   $223.71   $223.70   $223.70  
  Purchase #3 $171.36   4.254%   $178.6497   $178.65   $178.65   $178.60  
  Purchase #4 $44.31   10.722%   $49.0609   $49.06   $49.05   $49.10  
  Purchase #5 $128.29   10.131%   $141.2871   $141.29   $141.30   $141.30  
  Purchase #6 $114.96   4.525%   $120.1619   $120.16   $120.15   $120.20  
  Purchase #7 $160.98   8.662%   $174.9241   $174.92   $174.90   $174.90  
  7 purchase totals = $977.38       $1,068.2950   $1,068.29   $1,068.25   $1,068.30