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 $137.41   8.112%   $148.5567   $148.56   $148.55   $148.60  
  Purchase #2 $86.78   6.765%   $92.6507   $92.65   $92.65   $92.70  
  Purchase #3 $35.57   6.816%   $37.9945   $37.99   $38.00   $38.00  
  Purchase #4 $102.51   10.742%   $113.5216   $113.52   $113.50   $113.50  
  Purchase #5 $204.35   12.139%   $229.156   $229.16   $229.15   $229.20  
  Purchase #6 $14.48   4.104%   $15.0743   $15.07   $15.05   $15.10  
  Purchase #7 $56.98   8.158%   $61.6284   $61.63   $61.65   $61.60  
  7 purchase totals = $638.08       $698.5822   $698.58   $698.55   $698.70