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 $54.93   7.513%   $59.0569   $59.06   $59.05   $59.10  
  Purchase #2 $194.64   6.163%   $206.6357   $206.64   $206.65   $206.60  
  Purchase #3 $170.97   11.668%   $190.9188   $190.92   $190.90   $190.90  
  Purchase #4 $81.78   3.158%   $84.3626   $84.36   $84.35   $84.40  
  Purchase #5 $49.25   12.321%   $55.3181   $55.32   $55.30   $55.30  
  Purchase #6 $235.67   11.339%   $262.3926   $262.39   $262.40   $262.40  
  Purchase #7 $200.87   8.755%   $218.4562   $218.46   $218.45   $218.50  
  7 purchase totals = $988.11       $1,077.1409   $1,077.15   $1,077.10   $1,077.20