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 $120.65   11.264%   $134.24   $134.24   $134.25   $134.20  
  Purchase #2 $111.51   10.603%   $123.3334   $123.33   $123.35   $123.30  
  Purchase #3 $46.57   11.613%   $51.9782   $51.98   $52.00   $52.00  
  Purchase #4 $21.52   11.682%   $24.034   $24.03   $24.05   $24.00  
  Purchase #5 $28.49   7.336%   $30.58   $30.58   $30.60   $30.60  
  Purchase #6 $102.64   4.194%   $106.9447   $106.94   $106.95   $106.90  
  Purchase #7 $209.41   8.173%   $226.5251   $226.53   $226.55   $226.50  
  7 purchase totals = $640.79       $697.6354   $697.63   $697.75   $697.50