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 $235.89   12.743%   $265.9495   $265.95   $265.95   $265.90  
  Purchase #2 $51.36   3.803%   $53.3132   $53.31   $53.30   $53.30  
  Purchase #3 $176.50   7.590%   $189.8964   $189.90   $189.90   $189.90  
  Purchase #4 $61.87   10.250%   $68.2117   $68.21   $68.20   $68.20  
  Purchase #5 $107.37   10.508%   $118.6524   $118.65   $118.65   $118.70  
  Purchase #6 $158.85   11.547%   $177.1924   $177.19   $177.20   $177.20  
  Purchase #7 $45.57   9.346%   $49.829   $49.83   $49.85   $49.80  
  7 purchase totals = $837.41       $923.0446   $923.04   $923.05   $923.00