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 $135.95   5.485%   $143.4069   $143.41   $143.40   $143.40  
  Purchase #2 $174.96   5.534%   $184.6423   $184.64   $184.65   $184.60  
  Purchase #3 $243.99   3.745%   $253.1274   $253.13   $253.15   $253.10  
  Purchase #4 $49.58   5.807%   $52.4591   $52.46   $52.45   $52.50  
  Purchase #5 $11.71   12.630%   $13.189   $13.19   $13.20   $13.20  
  Purchase #6 $156.86   5.827%   $166.0002   $166.00   $166.00   $166.00  
  Purchase #7 $198.88   5.290%   $209.4008   $209.40   $209.40   $209.40  
  7 purchase totals = $971.93       $1,022.2257   $1,022.23   $1,022.25   $1,022.20