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 $58.34   7.699%   $62.8316   $62.83   $62.85   $62.80  
  Purchase #2 $135.61   8.665%   $147.3606   $147.36   $147.35   $147.40  
  Purchase #3 $217.98   9.323%   $238.3023   $238.30   $238.30   $238.30  
  Purchase #4 $241.39   9.610%   $264.5876   $264.59   $264.60   $264.60  
  Purchase #5 $60.44   6.727%   $64.5058   $64.51   $64.50   $64.50  
  Purchase #6 $101.89   13.125%   $115.2631   $115.26   $115.25   $115.30  
  Purchase #7 $133.55   3.553%   $138.295   $138.30   $138.30   $138.30  
  7 purchase totals = $949.20       $1,031.1460   $1,031.15   $1,031.15   $1,031.20