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 $48.93   13.736%   $55.651   $55.65   $55.65   $55.70  
  Purchase #2 $22.72   10.804%   $25.1747   $25.17   $25.15   $25.20  
  Purchase #3 $210.69   11.147%   $234.1756   $234.18   $234.20   $234.20  
  Purchase #4 $80.52   7.744%   $86.7555   $86.76   $86.75   $86.80  
  Purchase #5 $107.74   5.575%   $113.7465   $113.75   $113.75   $113.70  
  Purchase #6 $228.76   8.109%   $247.3101   $247.31   $247.30   $247.30  
  Purchase #7 $50.88   7.380%   $54.6349   $54.63   $54.65   $54.60  
  7 purchase totals = $750.24       $817.4483   $817.45   $817.45   $817.50