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 $69.77   8.153%   $75.4583   $75.46   $75.45   $75.50  
  Purchase #2 $41.79   3.339%   $43.1854   $43.19   $43.20   $43.20  
  Purchase #3 $134.50   7.274%   $144.2835   $144.28   $144.30   $144.30  
  Purchase #4 $175.97   5.839%   $186.2449   $186.24   $186.25   $186.20  
  Purchase #5 $161.41   12.739%   $181.972   $181.97   $181.95   $182.00  
  Purchase #6 $187.25   3.654%   $194.0921   $194.09   $194.10   $194.10  
  Purchase #7 $128.98   5.820%   $136.4866   $136.49   $136.50   $136.50  
  7 purchase totals = $899.67       $961.7228   $961.72   $961.75   $961.80