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 $193.88   11.543%   $216.2596   $216.26   $216.25   $216.30  
  Purchase #2 $179.37   8.487%   $194.5931   $194.59   $194.60   $194.60  
  Purchase #3 $99.37   8.635%   $107.9506   $107.95   $107.95   $108.00  
  Purchase #4 $32.38   13.744%   $36.8303   $36.83   $36.85   $36.80  
  Purchase #5 $23.52   5.730%   $24.8677   $24.87   $24.85   $24.90  
  Purchase #6 $223.94   5.764%   $236.8479   $236.85   $236.85   $236.80  
  Purchase #7 $50.95   12.531%   $57.3345   $57.33   $57.35   $57.30  
  7 purchase totals = $803.41       $874.6837   $874.68   $874.70   $874.70