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 $227.48   11.127%   $252.7917   $252.79   $252.80   $252.80  
  Purchase #2 $40.54   4.356%   $42.3059   $42.31   $42.30   $42.30  
  Purchase #3 $152.88   11.603%   $170.6187   $170.62   $170.60   $170.60  
  Purchase #4 $147.25   9.102%   $160.6527   $160.65   $160.65   $160.70  
  Purchase #5 $192.79   10.487%   $213.0079   $213.01   $213.00   $213.00  
  Purchase #6 $53.78   5.136%   $56.5421   $56.54   $56.55   $56.50  
  Purchase #7 $174.98   13.352%   $198.3433   $198.34   $198.35   $198.30  
  7 purchase totals = $989.70       $1,094.2623   $1,094.26   $1,094.25   $1,094.20