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 $181.84   9.209%   $198.5856   $198.59   $198.60   $198.60  
  Purchase #2 $122.32   9.831%   $134.3453   $134.35   $134.35   $134.30  
  Purchase #3 $190.58   7.724%   $205.3004   $205.30   $205.30   $205.30  
  Purchase #4 $234.53   8.710%   $254.9576   $254.96   $254.95   $255.00  
  Purchase #5 $81.32   3.185%   $83.91   $83.91   $83.90   $83.90  
  Purchase #6 $5.34   4.809%   $5.5968   $5.60   $5.60   $5.60  
  Purchase #7 $177.26   13.287%   $200.8125   $200.81   $200.80   $200.80  
  7 purchase totals = $993.19       $1,083.5082   $1,083.52   $1,083.50   $1,083.50