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 $96.27   11.791%   $107.6212   $107.62   $107.60   $107.60  
  Purchase #2 $63.71   6.714%   $67.9875   $67.99   $68.00   $68.00  
  Purchase #3 $119.68   7.865%   $129.0928   $129.09   $129.10   $129.10  
  Purchase #4 $237.74   13.556%   $269.968   $269.97   $269.95   $270.00  
  Purchase #5 $225.43   6.319%   $239.6749   $239.67   $239.65   $239.70  
  Purchase #6 $181.94   5.453%   $191.8612   $191.86   $191.85   $191.90  
  Purchase #7 $11.42   9.715%   $12.5295   $12.53   $12.55   $12.50  
  7 purchase totals = $936.19       $1,018.7351   $1,018.73   $1,018.70   $1,018.80