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 $54.33   12.534%   $61.1397   $61.14   $61.15   $61.10  
  Purchase #2 $55.92   8.735%   $60.8046   $60.80   $60.80   $60.80  
  Purchase #3 $232.38   13.204%   $263.0635   $263.06   $263.05   $263.10  
  Purchase #4 $72.52   7.232%   $77.7646   $77.76   $77.75   $77.80  
  Purchase #5 $235.31   10.479%   $259.9681   $259.97   $259.95   $260.00  
  Purchase #6 $63.34   8.855%   $68.9488   $68.95   $68.95   $68.90  
  Purchase #7 $212.50   4.830%   $222.7638   $222.76   $222.75   $222.80  
  7 purchase totals = $926.30       $1,014.4531   $1,014.44   $1,014.40   $1,014.50