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 $231.52   8.862%   $252.0373   $252.04   $252.05   $252.00  
  Purchase #2 $54.53   10.791%   $60.4143   $60.41   $60.40   $60.40  
  Purchase #3 $226.26   8.873%   $246.336   $246.34   $246.35   $246.30  
  Purchase #4 $58.57   5.761%   $61.9442   $61.94   $61.95   $61.90  
  Purchase #5 $207.63   8.639%   $225.5672   $225.57   $225.55   $225.60  
  Purchase #6 $9.59   12.748%   $10.8125   $10.81   $10.80   $10.80  
  Purchase #7 $87.64   13.575%   $99.5371   $99.54   $99.55   $99.50  
  7 purchase totals = $875.74       $956.6486   $956.65   $956.65   $956.50