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 $56.49   5.846%   $59.7924   $59.79   $59.80   $59.80  
  Purchase #2 $196.71   3.700%   $203.9883   $203.99   $204.00   $204.00  
  Purchase #3 $223.39   5.395%   $235.4419   $235.44   $235.45   $235.40  
  Purchase #4 $239.31   7.116%   $256.3393   $256.34   $256.35   $256.30  
  Purchase #5 $53.45   5.843%   $56.5731   $56.57   $56.55   $56.60  
  Purchase #6 $173.73   4.183%   $180.9971   $181.00   $181.00   $181.00  
  Purchase #7 $156.57   8.333%   $169.617   $169.62   $169.60   $169.60  
  7 purchase totals = $1,099.65       $1,162.7491   $1,162.75   $1,162.75   $1,162.70