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 $119.64   12.157%   $134.1846   $134.18   $134.20   $134.20  
  Purchase #2 $229.76   12.667%   $258.8637   $258.86   $258.85   $258.90  
  Purchase #3 $43.75   11.179%   $48.6408   $48.64   $48.65   $48.60  
  Purchase #4 $116.61   3.201%   $120.3427   $120.34   $120.35   $120.30  
  Purchase #5 $73.61   6.365%   $78.2953   $78.30   $78.30   $78.30  
  Purchase #6 $55.52   10.419%   $61.3046   $61.30   $61.30   $61.30  
  Purchase #7 $235.48   9.288%   $257.3514   $257.35   $257.35   $257.40  
  7 purchase totals = $874.37       $958.9831   $958.97   $959.00   $959.00