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 $108.74   9.436%   $119.0007   $119.00   $119.00   $119.00  
  Purchase #2 $25.99   8.166%   $28.1123   $28.11   $28.10   $28.10  
  Purchase #3 $189.44   3.413%   $195.9056   $195.91   $195.90   $195.90  
  Purchase #4 $112.40   7.651%   $120.9997   $121.00   $121.00   $121.00  
  Purchase #5 $43.46   8.526%   $47.1654   $47.17   $47.15   $47.20  
  Purchase #6 $22.57   8.621%   $24.5158   $24.52   $24.50   $24.50  
  Purchase #7 $200.68   5.811%   $212.3415   $212.34   $212.35   $212.30  
  7 purchase totals = $703.28       $748.0410   $748.05   $748.00   $748.00