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 $126.92   5.810%   $134.2941   $134.29   $134.30   $134.30  
  Purchase #2 $24.44   4.829%   $25.6202   $25.62   $25.60   $25.60  
  Purchase #3 $79.53   7.201%   $85.257   $85.26   $85.25   $85.30  
  Purchase #4 $142.57   9.420%   $156.0001   $156.00   $156.00   $156.00  
  Purchase #5 $200.59   9.595%   $219.8366   $219.84   $219.85   $219.80  
  Purchase #6 $161.49   3.586%   $167.281   $167.28   $167.30   $167.30  
  Purchase #7 $113.60   3.535%   $117.6158   $117.62   $117.60   $117.60  
  7 purchase totals = $849.14       $905.9048   $905.91   $905.90   $905.90