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 $62.78   13.364%   $71.1699   $71.17   $71.15   $71.20  
  Purchase #2 $181.83   13.127%   $205.6988   $205.70   $205.70   $205.70  
  Purchase #3 $177.37   8.819%   $193.0123   $193.01   $193.00   $193.00  
  Purchase #4 $127.57   5.344%   $134.3873   $134.39   $134.40   $134.40  
  Purchase #5 $120.30   7.241%   $129.0109   $129.01   $129.00   $129.00  
  Purchase #6 $39.49   7.552%   $42.4723   $42.47   $42.45   $42.50  
  Purchase #7 $237.57   7.273%   $254.8485   $254.85   $254.85   $254.80  
  7 purchase totals = $946.91       $1,030.6000   $1,030.60   $1,030.55   $1,030.60