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 $66.74   12.613%   $75.1579   $75.16   $75.15   $75.20  
  Purchase #2 $111.94   5.834%   $118.4706   $118.47   $118.45   $118.50  
  Purchase #3 $150.76   9.666%   $165.3325   $165.33   $165.35   $165.30  
  Purchase #4 $207.43   12.277%   $232.8962   $232.90   $232.90   $232.90  
  Purchase #5 $189.49   8.675%   $205.9283   $205.93   $205.95   $205.90  
  Purchase #6 $61.59   3.451%   $63.7155   $63.72   $63.70   $63.70  
  Purchase #7 $175.42   3.672%   $181.8614   $181.86   $181.85   $181.90  
  7 purchase totals = $963.37       $1,043.3624   $1,043.37   $1,043.35   $1,043.40