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 $71.99   6.155%   $76.421   $76.42   $76.40   $76.40  
  Purchase #2 $243.38   13.580%   $276.431   $276.43   $276.45   $276.40  
  Purchase #3 $59.66   9.517%   $65.3378   $65.34   $65.35   $65.30  
  Purchase #4 $160.72   4.750%   $168.3542   $168.35   $168.35   $168.40  
  Purchase #5 $211.68   6.336%   $225.092   $225.09   $225.10   $225.10  
  Purchase #6 $149.39   3.256%   $154.2541   $154.25   $154.25   $154.30  
  Purchase #7 $85.53   6.667%   $91.2323   $91.23   $91.25   $91.20  
  7 purchase totals = $982.35       $1,057.1224   $1,057.11   $1,057.15   $1,057.10