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 $45.92   6.827%   $49.055   $49.06   $49.05   $49.10  
  Purchase #2 $198.53   13.344%   $225.0218   $225.02   $225.00   $225.00  
  Purchase #3 $47.43   9.674%   $52.0184   $52.02   $52.00   $52.00  
  Purchase #4 $145.72   5.655%   $153.9605   $153.96   $153.95   $154.00  
  Purchase #5 $226.58   3.843%   $235.2875   $235.29   $235.30   $235.30  
  Purchase #6 $135.29   9.771%   $148.5092   $148.51   $148.50   $148.50  
  Purchase #7 $247.37   5.528%   $261.0446   $261.04   $261.05   $261.00  
  7 purchase totals = $1,046.84       $1,124.8970   $1,124.90   $1,124.85   $1,124.90