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 $165.55   11.172%   $184.0452   $184.05   $184.05   $184.00  
  Purchase #2 $207.92   11.239%   $231.2881   $231.29   $231.30   $231.30  
  Purchase #3 $74.41   4.370%   $77.6617   $77.66   $77.65   $77.70  
  Purchase #4 $130.61   5.828%   $138.222   $138.22   $138.20   $138.20  
  Purchase #5 $112.70   11.753%   $125.9456   $125.95   $125.95   $125.90  
  Purchase #6 $101.93   5.836%   $107.8786   $107.88   $107.90   $107.90  
  Purchase #7 $168.72   13.820%   $192.0371   $192.04   $192.05   $192.00  
  7 purchase totals = $961.84       $1,057.0783   $1,057.09   $1,057.10   $1,057.00