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 $176.62   12.299%   $198.3425   $198.34   $198.35   $198.30  
  Purchase #2 $96.81   9.867%   $106.3622   $106.36   $106.35   $106.40  
  Purchase #3 $237.82   10.772%   $263.438   $263.44   $263.45   $263.40  
  Purchase #4 $197.36   12.352%   $221.7379   $221.74   $221.75   $221.70  
  Purchase #5 $203.32   8.540%   $220.6835   $220.68   $220.70   $220.70  
  Purchase #6 $182.52   10.515%   $201.712   $201.71   $201.70   $201.70  
  Purchase #7 $52.93   10.610%   $58.5459   $58.55   $58.55   $58.50  
  7 purchase totals = $1,147.38       $1,270.8220   $1,270.82   $1,270.85   $1,270.70