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 $64.40   10.268%   $71.0126   $71.01   $71.00   $71.00  
  Purchase #2 $160.64   3.375%   $166.0616   $166.06   $166.05   $166.10  
  Purchase #3 $102.92   5.164%   $108.2348   $108.23   $108.25   $108.20  
  Purchase #4 $241.54   3.620%   $250.2837   $250.28   $250.30   $250.30  
  Purchase #5 $45.93   10.721%   $50.8542   $50.85   $50.85   $50.90  
  Purchase #6 $172.70   10.459%   $190.7627   $190.76   $190.75   $190.80  
  Purchase #7 $144.26   13.262%   $163.3918   $163.39   $163.40   $163.40  
  7 purchase totals = $932.39       $1,000.6014   $1,000.58   $1,000.60   $1,000.70