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 $25.25   5.219%   $26.5678   $26.57   $26.55   $26.60  
  Purchase #2 $76.66   11.609%   $85.5595   $85.56   $85.55   $85.60  
  Purchase #3 $116.88   8.231%   $126.5004   $126.50   $126.50   $126.50  
  Purchase #4 $156.54   9.294%   $171.0888   $171.09   $171.10   $171.10  
  Purchase #5 $245.57   7.213%   $263.283   $263.28   $263.30   $263.30  
  Purchase #6 $128.49   13.466%   $145.7925   $145.79   $145.80   $145.80  
  Purchase #7 $33.42   6.277%   $35.5178   $35.52   $35.50   $35.50  
  7 purchase totals = $782.81       $854.3098   $854.31   $854.30   $854.40