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 $53.89   10.108%   $59.3372   $59.34   $59.35   $59.30  
  Purchase #2 $207.64   4.167%   $216.2924   $216.29   $216.30   $216.30  
  Purchase #3 $189.40   3.434%   $195.904   $195.90   $195.90   $195.90  
  Purchase #4 $18.34   7.288%   $19.6766   $19.68   $19.70   $19.70  
  Purchase #5 $42.51   7.244%   $45.5894   $45.59   $45.60   $45.60  
  Purchase #6 $221.68   4.798%   $232.3162   $232.32   $232.30   $232.30  
  Purchase #7 $51.83   11.809%   $57.9506   $57.95   $57.95   $58.00  
  7 purchase totals = $785.29       $827.0664   $827.07   $827.10   $827.10