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 $84.49   13.849%   $96.191   $96.19   $96.20   $96.20  
  Purchase #2 $155.62   12.373%   $174.8749   $174.87   $174.85   $174.90  
  Purchase #3 $156.45   3.340%   $161.6754   $161.68   $161.70   $161.70  
  Purchase #4 $122.61   7.814%   $132.1907   $132.19   $132.20   $132.20  
  Purchase #5 $213.48   4.826%   $223.7825   $223.78   $223.80   $223.80  
  Purchase #6 $133.76   5.619%   $141.276   $141.28   $141.30   $141.30  
  Purchase #7 $95.33   4.301%   $99.4301   $99.43   $99.45   $99.40  
  7 purchase totals = $961.74       $1,029.4206   $1,029.42   $1,029.50   $1,029.50