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 $59.56   10.856%   $66.0258   $66.03   $66.05   $66.00  
  Purchase #2 $90.84   3.681%   $94.1838   $94.18   $94.20   $94.20  
  Purchase #3 $171.56   5.645%   $181.2446   $181.24   $181.25   $181.20  
  Purchase #4 $11.30   3.119%   $11.6524   $11.65   $11.65   $11.70  
  Purchase #5 $160.84   7.457%   $172.8338   $172.83   $172.85   $172.80  
  Purchase #6 $109.76   9.299%   $119.9666   $119.97   $119.95   $120.00  
  Purchase #7 $81.51   6.814%   $87.0641   $87.06   $87.05   $87.10  
  7 purchase totals = $685.37       $732.9711   $732.96   $733.00   $733.00