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 $246.88   7.751%   $266.0157   $266.02   $266.00   $266.00  
  Purchase #2 $111.26   5.826%   $117.742   $117.74   $117.75   $117.70  
  Purchase #3 $55.99   13.146%   $63.3504   $63.35   $63.35   $63.40  
  Purchase #4 $212.36   10.463%   $234.5792   $234.58   $234.60   $234.60  
  Purchase #5 $110.52   6.396%   $117.5889   $117.59   $117.60   $117.60  
  Purchase #6 $220.38   5.855%   $233.2832   $233.28   $233.30   $233.30  
  Purchase #7 $176.35   12.162%   $197.7977   $197.80   $197.80   $197.80  
  7 purchase totals = $1,133.74       $1,230.3571   $1,230.36   $1,230.40   $1,230.40