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 $220.86   7.654%   $237.7646   $237.76   $237.75   $237.80  
  Purchase #2 $159.57   13.155%   $180.5614   $180.56   $180.55   $180.60  
  Purchase #3 $147.65   3.617%   $152.9905   $152.99   $153.00   $153.00  
  Purchase #4 $34.50   6.473%   $36.7332   $36.73   $36.75   $36.70  
  Purchase #5 $116.60   10.291%   $128.5993   $128.60   $128.60   $128.60  
  Purchase #6 $130.49   11.348%   $145.298   $145.30   $145.30   $145.30  
  Purchase #7 $62.54   7.660%   $67.3306   $67.33   $67.35   $67.30  
  7 purchase totals = $872.21       $949.2776   $949.27   $949.30   $949.30