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 $120.68   4.307%   $125.8777   $125.88   $125.90   $125.90  
  Purchase #2 $139.44   5.535%   $147.158   $147.16   $147.15   $147.20  
  Purchase #3 $124.79   9.860%   $137.0943   $137.09   $137.10   $137.10  
  Purchase #4 $138.85   8.370%   $150.4717   $150.47   $150.45   $150.50  
  Purchase #5 $135.47   10.245%   $149.3489   $149.35   $149.35   $149.30  
  Purchase #6 $5.61   9.535%   $6.1449   $6.14   $6.15   $6.10  
  Purchase #7 $66.52   8.325%   $72.0578   $72.06   $72.05   $72.10  
  7 purchase totals = $731.36       $788.1533   $788.15   $788.15   $788.20