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 $42.26   3.279%   $43.6457   $43.65   $43.65   $43.60  
  Purchase #2 $191.91   5.543%   $202.5476   $202.55   $202.55   $202.50  
  Purchase #3 $201.73   3.766%   $209.3272   $209.33   $209.35   $209.30  
  Purchase #4 $114.33   3.230%   $118.0229   $118.02   $118.00   $118.00  
  Purchase #5 $176.81   5.539%   $186.6035   $186.60   $186.60   $186.60  
  Purchase #6 $182.31   13.459%   $206.8471   $206.85   $206.85   $206.80  
  Purchase #7 $48.84   8.869%   $53.1716   $53.17   $53.15   $53.20  
  7 purchase totals = $958.19       $1,020.1656   $1,020.17   $1,020.15   $1,020.00