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 $219.52   11.406%   $244.5585   $244.56   $244.55   $244.60  
  Purchase #2 $113.56   6.278%   $120.6893   $120.69   $120.70   $120.70  
  Purchase #3 $74.72   4.720%   $78.2468   $78.25   $78.25   $78.20  
  Purchase #4 $250.97   6.428%   $267.1024   $267.10   $267.10   $267.10  
  Purchase #5 $56.76   6.741%   $60.5862   $60.59   $60.60   $60.60  
  Purchase #6 $20.36   7.365%   $21.8595   $21.86   $21.85   $21.90  
  Purchase #7 $173.73   11.149%   $193.0992   $193.10   $193.10   $193.10  
  7 purchase totals = $909.62       $986.1419   $986.15   $986.15   $986.20