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 $94.96   3.227%   $98.0244   $98.02   $98.00   $98.00  
  Purchase #2 $209.99   10.650%   $232.3539   $232.35   $232.35   $232.40  
  Purchase #3 $224.30   10.499%   $247.8493   $247.85   $247.85   $247.80  
  Purchase #4 $127.60   12.684%   $143.7848   $143.78   $143.80   $143.80  
  Purchase #5 $85.61   5.621%   $90.4221   $90.42   $90.40   $90.40  
  Purchase #6 $81.77   6.782%   $87.3156   $87.32   $87.30   $87.30  
  Purchase #7 $159.42   11.204%   $177.2814   $177.28   $177.30   $177.30  
  7 purchase totals = $983.65       $1,077.0315   $1,077.02   $1,077.00   $1,077.00