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 $58.53   5.163%   $61.5519   $61.55   $61.55   $61.60  
  Purchase #2 $237.27   4.436%   $247.7953   $247.80   $247.80   $247.80  
  Purchase #3 $19.56   12.633%   $22.031   $22.03   $22.05   $22.00  
  Purchase #4 $10.37   10.575%   $11.4666   $11.47   $11.45   $11.50  
  Purchase #5 $144.38   13.241%   $163.4974   $163.50   $163.50   $163.50  
  Purchase #6 $165.36   13.180%   $187.1544   $187.15   $187.15   $187.20  
  Purchase #7 $110.67   9.287%   $120.9479   $120.95   $120.95   $120.90  
  7 purchase totals = $746.14       $814.4445   $814.45   $814.45   $814.50