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 $248.87   4.829%   $260.8879   $260.89   $260.90   $260.90  
  Purchase #2 $50.96   3.323%   $52.6534   $52.65   $52.65   $52.70  
  Purchase #3 $163.64   12.449%   $184.0115   $184.01   $184.00   $184.00  
  Purchase #4 $243.78   6.153%   $258.7798   $258.78   $258.80   $258.80  
  Purchase #5 $184.50   10.688%   $204.2194   $204.22   $204.20   $204.20  
  Purchase #6 $155.50   6.607%   $165.7739   $165.77   $165.75   $165.80  
  Purchase #7 $215.49   6.456%   $229.402   $229.40   $229.40   $229.40  
  7 purchase totals = $1,262.74       $1,355.7279   $1,355.72   $1,355.70   $1,355.80