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 $157.67   5.306%   $166.036   $166.04   $166.05   $166.00  
  Purchase #2 $241.61   12.692%   $272.2751   $272.28   $272.30   $272.30  
  Purchase #3 $108.83   7.864%   $117.3884   $117.39   $117.40   $117.40  
  Purchase #4 $228.87   12.173%   $256.7303   $256.73   $256.75   $256.70  
  Purchase #5 $105.62   6.266%   $112.2381   $112.24   $112.25   $112.20  
  Purchase #6 $163.74   10.309%   $180.62   $180.62   $180.60   $180.60  
  Purchase #7 $210.60   8.358%   $228.2019   $228.20   $228.20   $228.20  
  7 purchase totals = $1,216.94       $1,333.4898   $1,333.50   $1,333.55   $1,333.40