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 $181.70   11.151%   $201.9614   $201.96   $201.95   $202.00  
  Purchase #2 $192.42   7.207%   $206.2877   $206.29   $206.30   $206.30  
  Purchase #3 $34.88   4.430%   $36.4252   $36.43   $36.45   $36.40  
  Purchase #4 $37.49   7.374%   $40.2545   $40.25   $40.25   $40.30  
  Purchase #5 $226.57   12.402%   $254.6692   $254.67   $254.65   $254.70  
  Purchase #6 $55.79   5.813%   $59.0331   $59.03   $59.05   $59.00  
  Purchase #7 $59.55   3.726%   $61.7688   $61.77   $61.75   $61.80  
  7 purchase totals = $788.40       $860.3999   $860.40   $860.40   $860.50