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 $125.54   13.873%   $142.9562   $142.96   $142.95   $143.00  
  Purchase #2 $212.89   12.352%   $239.1862   $239.19   $239.20   $239.20  
  Purchase #3 $81.81   6.173%   $86.8601   $86.86   $86.85   $86.90  
  Purchase #4 $68.47   8.582%   $74.3461   $74.35   $74.35   $74.30  
  Purchase #5 $116.74   6.864%   $124.753   $124.75   $124.75   $124.80  
  Purchase #6 $233.66   8.482%   $253.479   $253.48   $253.50   $253.50  
  Purchase #7 $139.46   11.817%   $155.94   $155.94   $155.95   $155.90  
  7 purchase totals = $978.57       $1,077.5206   $1,077.53   $1,077.55   $1,077.60