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 $245.33   9.332%   $268.2242   $268.22   $268.20   $268.20  
  Purchase #2 $223.75   13.682%   $254.3635   $254.36   $254.35   $254.40  
  Purchase #3 $63.84   3.369%   $65.9908   $65.99   $66.00   $66.00  
  Purchase #4 $73.75   6.814%   $78.7753   $78.78   $78.80   $78.80  
  Purchase #5 $227.88   8.533%   $247.325   $247.33   $247.35   $247.30  
  Purchase #6 $127.54   9.158%   $139.2201   $139.22   $139.20   $139.20  
  Purchase #7 $145.97   13.131%   $165.1373   $165.14   $165.15   $165.10  
  7 purchase totals = $1,108.06       $1,219.0362   $1,219.04   $1,219.05   $1,219.00