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 $217.80   13.386%   $246.9547   $246.95   $246.95   $247.00  
  Purchase #2 $54.62   6.613%   $58.232   $58.23   $58.25   $58.20  
  Purchase #3 $212.39   13.439%   $240.9331   $240.93   $240.95   $240.90  
  Purchase #4 $48.89   13.826%   $55.6495   $55.65   $55.65   $55.60  
  Purchase #5 $221.97   6.115%   $235.5435   $235.54   $235.55   $235.50  
  Purchase #6 $81.59   13.440%   $92.5557   $92.56   $92.55   $92.60  
  Purchase #7 $203.92   7.121%   $218.4411   $218.44   $218.45   $218.40  
  7 purchase totals = $1,041.18       $1,148.3096   $1,148.30   $1,148.35   $1,148.20