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 $74.91   10.587%   $82.8407   $82.84   $82.85   $82.80  
  Purchase #2 $24.79   13.291%   $28.0848   $28.08   $28.10   $28.10  
  Purchase #3 $51.79   8.633%   $56.261   $56.26   $56.25   $56.30  
  Purchase #4 $198.63   5.237%   $209.0323   $209.03   $209.05   $209.00  
  Purchase #5 $206.95   5.182%   $217.6741   $217.67   $217.65   $217.70  
  Purchase #6 $222.63   5.873%   $235.7051   $235.71   $235.70   $235.70  
  Purchase #7 $49.99   12.708%   $56.3427   $56.34   $56.35   $56.30  
  7 purchase totals = $829.69       $885.9407   $885.93   $885.95   $885.90