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 $23.93   6.295%   $25.4364   $25.44   $25.45   $25.40  
  Purchase #2 $47.65   9.760%   $52.3006   $52.30   $52.30   $52.30  
  Purchase #3 $212.68   11.157%   $236.4087   $236.41   $236.40   $236.40  
  Purchase #4 $113.34   7.655%   $122.0162   $122.02   $122.00   $122.00  
  Purchase #5 $116.81   12.869%   $131.8423   $131.84   $131.85   $131.80  
  Purchase #6 $141.60   10.483%   $156.4439   $156.44   $156.45   $156.40  
  Purchase #7 $45.83   5.378%   $48.2947   $48.29   $48.30   $48.30  
  7 purchase totals = $701.84       $772.7428   $772.74   $772.75   $772.60