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 $246.60   5.861%   $261.0532   $261.05   $261.05   $261.10  
  Purchase #2 $203.50   7.133%   $218.0157   $218.02   $218.00   $218.00  
  Purchase #3 $24.68   7.657%   $26.5697   $26.57   $26.55   $26.60  
  Purchase #4 $33.97   7.378%   $36.4763   $36.48   $36.50   $36.50  
  Purchase #5 $80.93   8.697%   $87.9685   $87.97   $87.95   $88.00  
  Purchase #6 $182.42   11.683%   $203.7321   $203.73   $203.75   $203.70  
  Purchase #7 $213.89   9.865%   $234.9902   $234.99   $235.00   $235.00  
  7 purchase totals = $985.99       $1,068.8057   $1,068.81   $1,068.80   $1,068.90