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 $93.79   10.618%   $103.7486   $103.75   $103.75   $103.70  
  Purchase #2 $184.55   10.176%   $203.3298   $203.33   $203.35   $203.30  
  Purchase #3 $56.81   11.784%   $63.5045   $63.50   $63.50   $63.50  
  Purchase #4 $27.72   5.359%   $29.2055   $29.21   $29.20   $29.20  
  Purchase #5 $11.58   6.285%   $12.3078   $12.31   $12.30   $12.30  
  Purchase #6 $175.98   8.253%   $190.5036   $190.50   $190.50   $190.50  
  Purchase #7 $124.66   10.859%   $138.1968   $138.20   $138.20   $138.20  
  7 purchase totals = $675.09       $740.7966   $740.80   $740.80   $740.70