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 $222.70   13.831%   $253.5016   $253.50   $253.50   $253.50  
  Purchase #2 $217.52   13.132%   $246.0847   $246.08   $246.10   $246.10  
  Purchase #3 $206.78   8.634%   $224.6334   $224.63   $224.65   $224.60  
  Purchase #4 $171.66   5.434%   $180.988   $180.99   $181.00   $181.00  
  Purchase #5 $41.86   9.647%   $45.8982   $45.90   $45.90   $45.90  
  Purchase #6 $12.25   5.752%   $12.9546   $12.95   $12.95   $13.00  
  Purchase #7 $93.86   8.502%   $101.84   $101.84   $101.85   $101.80  
  7 purchase totals = $966.63       $1,065.9005   $1,065.89   $1,065.95   $1,065.90