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 $32.49   13.734%   $36.9522   $36.95   $36.95   $37.00  
  Purchase #2 $177.80   13.232%   $201.3265   $201.33   $201.35   $201.30  
  Purchase #3 $221.47   13.533%   $251.4415   $251.44   $251.45   $251.40  
  Purchase #4 $193.62   5.177%   $203.6437   $203.64   $203.65   $203.60  
  Purchase #5 $152.26   9.359%   $166.51   $166.51   $166.50   $166.50  
  Purchase #6 $117.46   8.661%   $127.6332   $127.63   $127.65   $127.60  
  Purchase #7 $155.44   11.292%   $172.9923   $172.99   $173.00   $173.00  
  7 purchase totals = $1,050.54       $1,160.4994   $1,160.49   $1,160.55   $1,160.40