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 $22.61   9.380%   $24.7308   $24.73   $24.75   $24.70  
  Purchase #2 $219.66   9.709%   $240.9868   $240.99   $241.00   $241.00  
  Purchase #3 $226.38   5.556%   $238.9577   $238.96   $238.95   $239.00  
  Purchase #4 $208.61   12.181%   $234.0208   $234.02   $234.00   $234.00  
  Purchase #5 $153.93   5.582%   $162.5224   $162.52   $162.50   $162.50  
  Purchase #6 $218.30   9.461%   $238.9534   $238.95   $238.95   $239.00  
  Purchase #7 $102.95   3.389%   $106.439   $106.44   $106.45   $106.40  
  7 purchase totals = $1,152.44       $1,246.6109   $1,246.61   $1,246.60   $1,246.60