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 $201.98   6.838%   $215.7914   $215.79   $215.80   $215.80  
  Purchase #2 $24.92   5.416%   $26.2697   $26.27   $26.25   $26.30  
  Purchase #3 $160.55   6.304%   $170.6711   $170.67   $170.65   $170.70  
  Purchase #4 $237.93   6.698%   $253.8666   $253.87   $253.85   $253.90  
  Purchase #5 $144.25   6.465%   $153.5758   $153.58   $153.60   $153.60  
  Purchase #6 $169.46   12.172%   $190.0867   $190.09   $190.10   $190.10  
  Purchase #7 $167.73   8.763%   $182.4282   $182.43   $182.45   $182.40  
  7 purchase totals = $1,106.82       $1,192.6895   $1,192.70   $1,192.70   $1,192.80