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 $79.44   7.432%   $85.344   $85.34   $85.35   $85.30  
  Purchase #2 $111.37   7.491%   $119.7127   $119.71   $119.70   $119.70  
  Purchase #3 $224.46   10.710%   $248.4997   $248.50   $248.50   $248.50  
  Purchase #4 $166.34   9.758%   $182.5715   $182.57   $182.55   $182.60  
  Purchase #5 $83.29   11.758%   $93.0832   $93.08   $93.10   $93.10  
  Purchase #6 $187.55   4.741%   $196.4417   $196.44   $196.45   $196.40  
  Purchase #7 $102.74   5.771%   $108.6691   $108.67   $108.65   $108.70  
  7 purchase totals = $955.19       $1,034.3219   $1,034.31   $1,034.30   $1,034.30