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 $245.31   5.769%   $259.4619   $259.46   $259.45   $259.50  
  Purchase #2 $106.80   3.614%   $110.6598   $110.66   $110.65   $110.70  
  Purchase #3 $24.85   4.139%   $25.8785   $25.88   $25.90   $25.90  
  Purchase #4 $133.55   8.455%   $144.8417   $144.84   $144.85   $144.80  
  Purchase #5 $203.93   10.593%   $225.5323   $225.53   $225.55   $225.50  
  Purchase #6 $69.36   8.727%   $75.413   $75.41   $75.40   $75.40  
  Purchase #7 $137.53   11.724%   $153.654   $153.65   $153.65   $153.70  
  7 purchase totals = $921.33       $995.4412   $995.43   $995.45   $995.50