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 $227.85   9.860%   $250.316   $250.32   $250.30   $250.30  
  Purchase #2 $207.49   10.352%   $228.9694   $228.97   $228.95   $229.00  
  Purchase #3 $147.85   6.209%   $157.03   $157.03   $157.05   $157.00  
  Purchase #4 $57.98   6.592%   $61.802   $61.80   $61.80   $61.80  
  Purchase #5 $203.90   6.171%   $216.4827   $216.48   $216.50   $216.50  
  Purchase #6 $56.45   8.589%   $61.2985   $61.30   $61.30   $61.30  
  Purchase #7 $120.95   10.699%   $133.8904   $133.89   $133.90   $133.90  
  7 purchase totals = $1,022.47       $1,109.7890   $1,109.79   $1,109.80   $1,109.80