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 $137.52   5.541%   $145.14   $145.14   $145.15   $145.10  
  Purchase #2 $22.94   9.653%   $25.1544   $25.15   $25.15   $25.20  
  Purchase #3 $44.69   7.121%   $47.8724   $47.87   $47.85   $47.90  
  Purchase #4 $110.51   4.524%   $115.5095   $115.51   $115.50   $115.50  
  Purchase #5 $59.70   13.503%   $67.7613   $67.76   $67.75   $67.80  
  Purchase #6 $245.72   4.736%   $257.3573   $257.36   $257.35   $257.40  
  Purchase #7 $95.55   5.235%   $100.552   $100.55   $100.55   $100.60  
  7 purchase totals = $716.63       $759.3469   $759.34   $759.30   $759.50