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 $87.67   6.526%   $93.3913   $93.39   $93.40   $93.40  
  Purchase #2 $243.75   11.309%   $271.3157   $271.32   $271.30   $271.30  
  Purchase #3 $48.93   13.241%   $55.4088   $55.41   $55.40   $55.40  
  Purchase #4 $61.72   9.831%   $67.7877   $67.79   $67.80   $67.80  
  Purchase #5 $87.41   13.171%   $98.9228   $98.92   $98.90   $98.90  
  Purchase #6 $220.72   5.613%   $233.109   $233.11   $233.10   $233.10  
  Purchase #7 $207.77   9.270%   $227.0303   $227.03   $227.05   $227.00  
  7 purchase totals = $957.97       $1,046.9656   $1,046.97   $1,046.95   $1,046.90