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 $42.53   5.652%   $44.9338   $44.93   $44.95   $44.90  
  Purchase #2 $241.37   11.258%   $268.5434   $268.54   $268.55   $268.50  
  Purchase #3 $11.90   9.361%   $13.014   $13.01   $13.00   $13.00  
  Purchase #4 $193.87   6.350%   $206.1807   $206.18   $206.20   $206.20  
  Purchase #5 $207.76   9.277%   $227.0339   $227.03   $227.05   $227.00  
  Purchase #6 $141.95   7.642%   $152.7978   $152.80   $152.80   $152.80  
  Purchase #7 $83.51   5.737%   $88.301   $88.30   $88.30   $88.30  
  7 purchase totals = $922.89       $1,000.8046   $1,000.79   $1,000.85   $1,000.70