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 $170.70   11.727%   $190.718   $190.72   $190.70   $190.70  
  Purchase #2 $163.69   12.312%   $183.8435   $183.84   $183.85   $183.80  
  Purchase #3 $23.52   9.748%   $25.8127   $25.81   $25.80   $25.80  
  Purchase #4 $77.34   13.149%   $87.5094   $87.51   $87.50   $87.50  
  Purchase #5 $143.73   4.464%   $150.1461   $150.15   $150.15   $150.10  
  Purchase #6 $170.41   5.511%   $179.8013   $179.80   $179.80   $179.80  
  Purchase #7 $24.58   8.252%   $26.6083   $26.61   $26.60   $26.60  
  7 purchase totals = $773.97       $844.4393   $844.44   $844.40   $844.30