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 $232.37   10.628%   $257.0663   $257.07   $257.05   $257.10  
  Purchase #2 $31.71   10.281%   $34.9701   $34.97   $34.95   $35.00  
  Purchase #3 $166.35   13.358%   $188.571   $188.57   $188.55   $188.60  
  Purchase #4 $227.71   9.181%   $248.6161   $248.62   $248.60   $248.60  
  Purchase #5 $127.29   13.287%   $144.203   $144.20   $144.20   $144.20  
  Purchase #6 $41.93   6.765%   $44.7666   $44.77   $44.75   $44.80  
  Purchase #7 $95.92   10.653%   $106.1384   $106.14   $106.15   $106.10  
  7 purchase totals = $923.28       $1,024.3315   $1,024.34   $1,024.25   $1,024.40