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 $167.41   8.472%   $181.593   $181.59   $181.60   $181.60  
  Purchase #2 $242.28   4.571%   $253.3546   $253.35   $253.35   $253.40  
  Purchase #3 $175.70   8.618%   $190.8418   $190.84   $190.85   $190.80  
  Purchase #4 $71.35   12.312%   $80.1346   $80.13   $80.15   $80.10  
  Purchase #5 $54.86   3.565%   $56.8158   $56.82   $56.80   $56.80  
  Purchase #6 $145.68   8.333%   $157.8195   $157.82   $157.80   $157.80  
  Purchase #7 $103.43   3.348%   $106.8928   $106.89   $106.90   $106.90  
  7 purchase totals = $960.71       $1,027.4521   $1,027.44   $1,027.45   $1,027.40