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 $86.42   11.364%   $96.2408   $96.24   $96.25   $96.20  
  Purchase #2 $45.93   9.421%   $50.2571   $50.26   $50.25   $50.30  
  Purchase #3 $227.30   5.727%   $240.3175   $240.32   $240.30   $240.30  
  Purchase #4 $63.96   3.172%   $65.9888   $65.99   $66.00   $66.00  
  Purchase #5 $207.43   7.333%   $222.6408   $222.64   $222.65   $222.60  
  Purchase #6 $118.39   3.756%   $122.8367   $122.84   $122.85   $122.80  
  Purchase #7 $112.49   7.282%   $120.6815   $120.68   $120.70   $120.70  
  7 purchase totals = $861.92       $918.9632   $918.97   $919.00   $918.90