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 $59.45   11.426%   $66.2428   $66.24   $66.25   $66.20  
  Purchase #2 $209.64   9.818%   $230.2225   $230.22   $230.20   $230.20  
  Purchase #3 $225.90   11.809%   $252.5765   $252.58   $252.60   $252.60  
  Purchase #4 $151.67   13.106%   $171.5479   $171.55   $171.55   $171.50  
  Purchase #5 $114.42   12.724%   $128.9788   $128.98   $129.00   $129.00  
  Purchase #6 $235.77   12.394%   $264.9913   $264.99   $265.00   $265.00  
  Purchase #7 $184.80   9.401%   $202.173   $202.17   $202.15   $202.20  
  7 purchase totals = $1,181.65       $1,316.7328   $1,316.73   $1,316.75   $1,316.70