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 $64.61   8.164%   $69.8848   $69.88   $69.90   $69.90  
  Purchase #2 $119.79   5.306%   $126.1461   $126.15   $126.15   $126.10  
  Purchase #3 $122.43   3.398%   $126.5902   $126.59   $126.60   $126.60  
  Purchase #4 $192.96   12.521%   $217.1205   $217.12   $217.10   $217.10  
  Purchase #5 $36.25   3.343%   $37.4618   $37.46   $37.45   $37.50  
  Purchase #6 $163.27   7.544%   $175.5871   $175.59   $175.60   $175.60  
  Purchase #7 $238.91   3.521%   $247.322   $247.32   $247.30   $247.30  
  7 purchase totals = $938.22       $1,000.1125   $1,000.11   $1,000.10   $1,000.10