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 $33.72   5.459%   $35.5608   $35.56   $35.55   $35.60  
  Purchase #2 $175.98   10.842%   $195.0598   $195.06   $195.05   $195.10  
  Purchase #3 $45.29   9.577%   $49.6274   $49.63   $49.65   $49.60  
  Purchase #4 $98.42   8.501%   $106.7867   $106.79   $106.80   $106.80  
  Purchase #5 $229.39   9.611%   $251.4367   $251.44   $251.45   $251.40  
  Purchase #6 $248.60   11.820%   $277.9845   $277.98   $278.00   $278.00  
  Purchase #7 $128.35   13.404%   $145.554   $145.55   $145.55   $145.60  
  7 purchase totals = $959.75       $1,062.0099   $1,062.01   $1,062.05   $1,062.10