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 $63.65   7.301%   $68.2971   $68.30   $68.30   $68.30  
  Purchase #2 $189.48   11.865%   $211.9618   $211.96   $211.95   $212.00  
  Purchase #3 $16.68   5.401%   $17.5809   $17.58   $17.60   $17.60  
  Purchase #4 $232.48   9.809%   $255.284   $255.28   $255.30   $255.30  
  Purchase #5 $192.93   3.114%   $198.9378   $198.94   $198.95   $198.90  
  Purchase #6 $222.48   7.566%   $239.3128   $239.31   $239.30   $239.30  
  Purchase #7 $46.99   6.682%   $50.1299   $50.13   $50.15   $50.10  
  7 purchase totals = $964.69       $1,041.5043   $1,041.50   $1,041.55   $1,041.50