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 $245.71   5.412%   $259.0078   $259.01   $259.00   $259.00  
  Purchase #2 $196.65   3.840%   $204.2014   $204.20   $204.20   $204.20  
  Purchase #3 $54.71   13.185%   $61.9235   $61.92   $61.90   $61.90  
  Purchase #4 $210.42   11.437%   $234.4857   $234.49   $234.50   $234.50  
  Purchase #5 $82.89   10.403%   $91.513   $91.51   $91.50   $91.50  
  Purchase #6 $129.52   3.279%   $133.767   $133.77   $133.75   $133.80  
  Purchase #7 $59.59   7.552%   $64.0902   $64.09   $64.10   $64.10  
  7 purchase totals = $979.49       $1,048.9886   $1,048.99   $1,048.95   $1,049.00