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 $62.68   11.182%   $69.6889   $69.69   $69.70   $69.70  
  Purchase #2 $31.61   3.810%   $32.8143   $32.81   $32.80   $32.80  
  Purchase #3 $73.59   6.653%   $78.4859   $78.49   $78.50   $78.50  
  Purchase #4 $216.81   4.627%   $226.8418   $226.84   $226.85   $226.80  
  Purchase #5 $37.74   4.443%   $39.4168   $39.42   $39.40   $39.40  
  Purchase #6 $161.26   12.566%   $181.5239   $181.52   $181.50   $181.50  
  Purchase #7 $21.72   7.150%   $23.273   $23.27   $23.25   $23.30  
  7 purchase totals = $605.41       $652.0446   $652.04   $652.00   $652.00