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 $36.53   6.676%   $38.9687   $38.97   $38.95   $39.00  
  Purchase #2 $234.98   10.282%   $259.1406   $259.14   $259.15   $259.10  
  Purchase #3 $67.31   11.559%   $75.0904   $75.09   $75.10   $75.10  
  Purchase #4 $74.29   12.563%   $83.6231   $83.62   $83.60   $83.60  
  Purchase #5 $202.94   12.108%   $227.512   $227.51   $227.50   $227.50  
  Purchase #6 $177.59   5.832%   $187.947   $187.95   $187.95   $187.90  
  Purchase #7 $207.64   11.623%   $231.774   $231.77   $231.75   $231.80  
  7 purchase totals = $1,001.28       $1,104.0558   $1,104.05   $1,104.00   $1,104.00