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 $212.94   13.487%   $241.6592   $241.66   $241.65   $241.70  
  Purchase #2 $55.46   12.476%   $62.3792   $62.38   $62.40   $62.40  
  Purchase #3 $150.56   11.416%   $167.7479   $167.75   $167.75   $167.70  
  Purchase #4 $61.66   6.517%   $65.6784   $65.68   $65.70   $65.70  
  Purchase #5 $192.99   9.605%   $211.5267   $211.53   $211.55   $211.50  
  Purchase #6 $245.26   5.481%   $258.7027   $258.70   $258.70   $258.70  
  Purchase #7 $131.76   6.651%   $140.5234   $140.52   $140.50   $140.50  
  7 purchase totals = $1,050.63       $1,148.2175   $1,148.22   $1,148.25   $1,148.20