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 $35.41   9.504%   $38.7754   $38.78   $38.80   $38.80  
  Purchase #2 $202.39   3.528%   $209.5303   $209.53   $209.55   $209.50  
  Purchase #3 $174.99   9.195%   $191.0803   $191.08   $191.10   $191.10  
  Purchase #4 $248.37   11.495%   $276.9201   $276.92   $276.90   $276.90  
  Purchase #5 $222.38   5.765%   $235.2002   $235.20   $235.20   $235.20  
  Purchase #6 $58.82   9.475%   $64.3932   $64.39   $64.40   $64.40  
  Purchase #7 $60.74   5.460%   $64.0564   $64.06   $64.05   $64.10  
  7 purchase totals = $1,003.10       $1,079.9559   $1,079.96   $1,080.00   $1,080.00