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 $67.59   5.459%   $71.2797   $71.28   $71.30   $71.30  
  Purchase #2 $220.95   12.148%   $247.791   $247.79   $247.80   $247.80  
  Purchase #3 $44.27   13.527%   $50.2584   $50.26   $50.25   $50.30  
  Purchase #4 $53.88   7.381%   $57.8569   $57.86   $57.85   $57.90  
  Purchase #5 $239.94   9.459%   $262.6359   $262.64   $262.65   $262.60  
  Purchase #6 $162.64   7.797%   $175.321   $175.32   $175.30   $175.30  
  Purchase #7 $31.51   8.584%   $34.2148   $34.21   $34.20   $34.20  
  7 purchase totals = $820.78       $899.3577   $899.36   $899.35   $899.40