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 $64.58   13.809%   $73.4979   $73.50   $73.50   $73.50  
  Purchase #2 $223.98   8.529%   $243.0833   $243.08   $243.10   $243.10  
  Purchase #3 $245.69   11.140%   $273.0599   $273.06   $273.05   $273.10  
  Purchase #4 $114.46   13.600%   $130.0266   $130.03   $130.05   $130.00  
  Purchase #5 $8.93   8.532%   $9.6919   $9.69   $9.70   $9.70  
  Purchase #6 $97.95   5.350%   $103.1903   $103.19   $103.20   $103.20  
  Purchase #7 $208.86   9.621%   $228.9544   $228.95   $228.95   $229.00  
  7 purchase totals = $964.45       $1,061.5043   $1,061.50   $1,061.55   $1,061.60