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 $133.65   12.703%   $150.6276   $150.63   $150.65   $150.60  
  Purchase #2 $41.37   6.254%   $43.9573   $43.96   $43.95   $44.00  
  Purchase #3 $187.70   6.431%   $199.771   $199.77   $199.75   $199.80  
  Purchase #4 $139.92   6.355%   $148.8119   $148.81   $148.80   $148.80  
  Purchase #5 $113.55   6.463%   $120.8887   $120.89   $120.90   $120.90  
  Purchase #6 $59.27   3.209%   $61.172   $61.17   $61.15   $61.20  
  Purchase #7 $130.46   5.781%   $138.0019   $138.00   $138.00   $138.00  
  7 purchase totals = $805.92       $863.2304   $863.23   $863.20   $863.30