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 $32.86   13.255%   $37.2156   $37.22   $37.20   $37.20  
  Purchase #2 $223.87   8.378%   $242.6258   $242.63   $242.65   $242.60  
  Purchase #3 $164.84   10.263%   $181.7575   $181.76   $181.75   $181.80  
  Purchase #4 $183.87   11.481%   $204.9801   $204.98   $205.00   $205.00  
  Purchase #5 $52.75   10.626%   $58.3552   $58.36   $58.35   $58.40  
  Purchase #6 $95.27   6.556%   $101.5159   $101.52   $101.50   $101.50  
  Purchase #7 $49.67   7.161%   $53.2269   $53.23   $53.25   $53.20  
  7 purchase totals = $803.13       $879.6770   $879.70   $879.70   $879.70