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 $51.28   13.791%   $58.352   $58.35   $58.35   $58.40  
  Purchase #2 $101.25   9.300%   $110.6663   $110.67   $110.65   $110.70  
  Purchase #3 $36.53   6.734%   $38.9899   $38.99   $39.00   $39.00  
  Purchase #4 $75.55   7.116%   $80.9261   $80.93   $80.95   $80.90  
  Purchase #5 $110.91   6.508%   $118.128   $118.13   $118.15   $118.10  
  Purchase #6 $227.76   5.597%   $240.5077   $240.51   $240.50   $240.50  
  Purchase #7 $32.52   8.723%   $35.3567   $35.36   $35.35   $35.40  
  7 purchase totals = $635.80       $682.9267   $682.94   $682.95   $683.00