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 $55.45   13.252%   $62.7982   $62.80   $62.80   $62.80  
  Purchase #2 $226.53   10.585%   $250.5082   $250.51   $250.50   $250.50  
  Purchase #3 $20.62   11.190%   $22.9274   $22.93   $22.95   $22.90  
  Purchase #4 $211.87   10.550%   $234.2223   $234.22   $234.20   $234.20  
  Purchase #5 $184.64   12.461%   $207.648   $207.65   $207.65   $207.60  
  Purchase #6 $60.60   10.840%   $67.169   $67.17   $67.15   $67.20  
  Purchase #7 $150.42   3.157%   $155.1688   $155.17   $155.15   $155.20  
  7 purchase totals = $910.13       $1,000.4419   $1,000.45   $1,000.40   $1,000.40