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 $65.35   6.811%   $69.801   $69.80   $69.80   $69.80  
  Purchase #2 $199.73   6.303%   $212.319   $212.32   $212.30   $212.30  
  Purchase #3 $231.83   10.242%   $255.574   $255.57   $255.55   $255.60  
  Purchase #4 $58.87   10.368%   $64.9736   $64.97   $64.95   $65.00  
  Purchase #5 $163.67   5.739%   $173.063   $173.06   $173.05   $173.10  
  Purchase #6 $91.41   7.299%   $98.082   $98.08   $98.10   $98.10  
  Purchase #7 $122.96   3.187%   $126.8787   $126.88   $126.90   $126.90  
  7 purchase totals = $933.82       $1,000.6913   $1,000.68   $1,000.65   $1,000.80